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Chemistry Unit 2 > Concentration > Flashcards

Concentration Flashcards

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1
Q

what are the common concentration units?

A
  • molL-1 (M)
  • gL-1
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2
Q

what is a great solvent?

A

Water is a great solvent, so many things will dissolve in it!

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3
Q

what is a solution?

A

When solutes are soluble (dissolve) in a solvent a solution is formed.

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4
Q

characteristics of solutions?

A

Solutions are transparent and consistent throughout.

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5
Q

define concentration

A

Concentration is a ratio comparing the amount of solute to the amount of solvent in a solution.

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6
Q

what is a solution when it has a little solute?

A

dilute

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7
Q

what is a solution when it has a lot solute?

A

concentrated

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8
Q

How to express concentration?

A

Concentration can be communicated in a number of ways:
- Using colour for different concentrations (solute must be coloured)
- Using dots for different concentration solutions
- Using numerical values (with units)

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9
Q

concentration worded equation

A

Conc = amount of solute/amount of solvent

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10
Q

what are different ways to measure the “amount” of solute and solvent?

A
  • using mass (g)
  • using volume (L) or (mL)
  • using moles (n)
  • as percentages
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11
Q

what will using different amount unit do the concentration unit?

A

Using different “amount” units will change the concentration unit.

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12
Q

what is gL-1?

A

Conc (gL-1) = mass of solute (g)/volume of solvent (L)
C = m/V

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13
Q

when is gL-1 used?

A

These units are commonly used if the solute is a mixture (formula is not known) or for everyday life (non-chemistry) examples.

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14
Q

what is molL-1?

A

Conc (molL-1) = moles of solute (mol)/volume of solvent (L)
C = n/V

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15
Q

when is molL-1 used?

A
  • Most common concentration units in chem!
  • Solute must be pure (so the formula is known).
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16
Q

how are moles calculated?

A

n = m/M

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17
Q

how is molL-1 abbreviated?

A

Unit molL-1 sometimes abbreviated to M (Molarity)

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18
Q

what do you need to make sure when calculating concentration?

A

that the units are correct

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19
Q

what happens when salts dissolve?

A

When salts dissolve their ions become free to move in the solution.

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20
Q

what else can you calculate the conc of other than the salt?

A

Often we calculate the conc of the salt but you can also calculate the conc of either the + or - ions in the solution.

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21
Q

what does calculate the conc of ions in solution require?

A

This requires ratios to be considered.

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22
Q

where does water go in dissolving equations?

A

over the arrow

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23
Q

what are the new key glassware for a titration?

A
  • volumetric flask
  • conical flask
  • pipette
  • burette and stand
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24
Q

define standard solution

A

A standard solution is a solution (typically made of a dissolved ionic salt/acid/base) with an accurately known concentration.

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25
Q

how do you make an accurately known conc?

A

To have an accurately known concentration you need to use glassware where the volume can be accurately measured. This means using a volumetric flask. Beakers and measuring cylinders are not accurate enough!

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26
Q

what size are volumetric flasks?

A

Volumetric flasks come in a range of sizes.

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27
Q

how can the volume be accurate known in a volumetric flask?

A

The volume can be accurately known when the meniscus sits correctly relative to the graduated mark on the flask.

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28
Q

what do you need to be careful of in volumetric flask?

A

Avoid parallax error by coming down to the level of the graduated mark.

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29
Q

Steps for making a standard solution?

A
  • Weighing Solute
  • Dissolve solute in small amount of solvent, warming if necessary
  • Transfer to standard flask
  • Rinse all solution into flask with more solvent
  • Carefully make up to the mark on the flask
  • Stopper and shake
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30
Q

as weighing out a exact mass is hard is it okay if its a little bit out?

A

Yes! Simply calculate the exact concentration you will have based on your exact mass.

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31
Q

what is a primary standard?

A

Ideally a standard solution is made using a primary standard, this is a chemical which meets a number of key criteria:
- High state of purity
- Accurately known formula
- Stable. Does not react with chemicals in the air. Does not lose/gain water/carbon dioxide from the air over time
- Cheap and readily available
- High molar mass (minimises the significance of weighing errors)

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32
Q

what happens to a solution that not a primary standard in titration?

A

A solution that’s not a primary standard must have its concentration verified against a primary standard using a titration prior to use.

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33
Q

define titration

A

A titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution.

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34
Q

what is a pipette used for?

A

A pipette is used to transfer a known volume of a solution into a conical flask.

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35
Q

what type of solution does a pipette transfer?

A

This solution is often a standard solution that’s been prepared in a volumetric flask.

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36
Q

how much volume does a pipette have?

A

Pipettes come in a range of set volumes, typically 10mL, 20mL or 25mL.

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37
Q

what is a pipette filler needed for?

A

A pipette filler is needed to fill the solution into the pipette.

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38
Q

how can volume be accurately known in a volumetric flask?

A

The volume can be accurately known when the meniscus sits correctly relative to the graduated mark on the flask.

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39
Q

how to use a pipette?

A

Allow the solution to run into the conical flask under gravity. You will notice a small amount of solution will remain in the tip of the pipette, this is normal. Tap pipette to the side of the flask but do not force the last drop into the flask!

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40
Q

what are the less common concentration units?

A

As a %:
- % (m/m)
- % (m/v)
- % (v/v)

  • ppm
  • ppb
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41
Q

what units are most used in chem?

A

The units of molL-1 and gL-1 are the most commonly used in chemistry.

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42
Q

when in a non chemistry context what does conc need to be?

A

When solutions are used in a non-chemistry context such as cosmetics, household cleaners, alcoholic drinks etc a more easily understood way of expressing concn is needed. This is when using a % is useful.

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43
Q

what is the general format for percentages?

A

% = thing you’re interested in/the total available x 100

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44
Q

how do you calculate % (m/m)?

A

% = mass solute (g)/mass solvent (g) x 100

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45
Q

how do you calculate % (m/v)?

A

% = mass solute (g)/vol solvent (mL) x 100

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46
Q

how do you calculate % (v/v)?

A

% = vol solute (mL)/vol solvent (mL) x 100

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47
Q

what unit does percentage calculation have?

A

Notice the unusual unit for volume in these % calculations.

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48
Q

what does pure water equate to?

A

Remember that for pure water 1g = 1mL

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49
Q

what is ppm?

A

parts per million

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50
Q

what is the unit of ppm?

A

Unit typically mgL-1 or µgmL-1

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51
Q

what is ppb?

A

parts per million

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52
Q

what is the unit of ppm?

A

Unit typically µgkg-1

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53
Q

when are ppm and ppb used?

A

These units are typically used in environmental contexts when we are discussing small + very small amounts of solute in solvent.

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54
Q

how do you calculate ppm?

A
  • mass solute (mg)/mass solvent (kg or L)
  • mass solute (µg)/mass solvent (g or mL)
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55
Q

how do you calculate ppb?

A

mass solute (µg)/mass solvent (kg or L)

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56
Q

how much percent of seawater is fresh or salty?

A

2.6% of water on Earth is freshwater (eg lakes)
97.4% of water is salty water (eg oceans)

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57
Q

what is in our drinking water?

A

There are many different ionic salts dissolved into our drinking water. Some of these salts have no negative health impacts, while others have significant health impacts and must have their concentration in water closely monitored and controlled.

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58
Q

define contaminant?

A

A contaminant is an unwanted substance that makes water unsuitable for its intended use.

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59
Q

How do contaminant get into drinking water?

A
  • Direct discharge
  • Stormwater runoff
  • Groundwater contamination
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60
Q

define Direct discharge

A

discharge from factories, poorly maintained sewerage, agricultural and fertiliser waste

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61
Q

define Stormwater runoff

A

natural process of water running over land

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62
Q

define Groundwater contamination

A

buried contaminants seeping into underground water supplies

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63
Q

what are Heavy metal contaminants?

A
  • arsenic
  • cadium
  • chronium
    and more
    from industrial and aggircultural wastes, mining, manufacture and
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64
Q

what is solubility of ionic salts?

A

Ionic salts are not just soluble or insoluble.
The solubility of each ionic salt lies somewhere on a solubility continuum.

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65
Q

what is the solubility of ionic salts determined on?

A

How much (mass) of a particular salt (solute) will dissolve in the water is highly dependent both the volume of water available and the temperature of the water.

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66
Q

what happens to the solubility of ionic salts with temperature?

A

Most salts will be more soluble if more water is used, or the water is hotter.

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67
Q

how is solubility of ionic salts measured?

A

Solubility of ionic salts can be measured in g/100g of water.

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68
Q

what is g/100g of water showing?

A

This is a measure of how many grams of salt (mass) dissolve in 100g of water.

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69
Q

what is 100g of water?

A

Remembering that 1g = 1mL for water so this is really in 100mL of water.

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70
Q

what are the different types of solutions?

A
  • unsaturated solution
  • saturated solution
  • supersaturated solution
71
Q

what is an unsaturated solution?

A

There is less than the max amount of salt is dissolved (more salt could be added and successfully dissolve)

72
Q

what is a saturated solution?

A

This is exactly the max amount of salt dissolved (no more salt could be added and successfully dissolve)

73
Q

what is a supersaturated solution?

A

There is more than the max amount of salt you’d expect to dissolve at this temp and vol.

74
Q

what happens to solute in an unsaturated solution?

A

more solute dissolves

75
Q

what happens to solute in a saturated solution?

A

no more solute dissolves

76
Q

what happens to solute in a supersaturated solution?

A

becomes unstable, crystals form

77
Q

how do you form a supersaturated solution?

A
  1. Heat the water above the desired temp (eg 80oC)
  2. Dissolve as a large amount of salt at this higher temp
  3. Slowly allow solution to cool to desired temp (eg 60oC). There is now more than the max amount of salt you’d expect to dissolve at this temp and vol
78
Q

what is a characteristic of supersaturated solutions?

A

Supersaturated solutions are unstable, salt crystals can easily come out of solution (crystalise/precipitate).

79
Q

define Gravimetric analysis

A

Practical technique that uses mass to mass stoichiometry.

Quantitative analysis to find the amount (mass/%/conc) of dissolved substance in aqueous solution.

80
Q

what are the steps to gravimetric analysis?

A
  1. Record the mass of sample (mixture) to be analysed
  2. Dissolving the sample in water
  3. Adding a suitable chemical to form a precipitate
  4. Filtering to collect the precipitate (washing steps required)
  5. Repeatedly drying and weighing until constant mass of precipitate
81
Q

what are special considerations of gravimetric analysis?

A
  • Substance being analysed may already be dissolved, therefore start at step 2
  • Filtering at 2 may be needed
  • Washing at 4 required repeated ‘flushing’ precipitate with deionised water
  • Dry in an oven at 5 set to 105oC (evaporates water)
    as step 5 means constant mass means all water removed
  • Knowledge of solubility rules for ionic substances/salts is needed to select an appropriate chemical to add so that a precipitate is formed in step 3.
82
Q

what are the actions for gravimetric analysis that could causes an effect or no effect?

A
  • insoluble materials not filtered out before forming the precipitate
  • not enough of the precipitate-forming chemical added
  • forming a precipitate that is too soluble
  • forming extra precipitate due to the presence of other competing ions
  • weighing the precipitate before it is dry
  • not rinsing the precipitate before drying it
  • adding too much of the precipitate-causing chemical
  • using too much water for the initial dissolving
83
Q

what effect does insoluble materials not filtered out before forming the precipitate have and what is its reason?

A

overestimated, The apparent mass of the precipitate will increase.

84
Q

what effect does not enough of the precipitate-forming chemical added have and what is its reason?

A

underestimated, Not enough of the precipitate will form as some of the ions that are being analysed will remain in solution

85
Q

what effect does forming a precipitate that is too soluble have and what is its reason?

A

underestimated, Not all of the ions being analysed will be in the precipitate.

86
Q

what effect does forming extra precipitate due to the presence of other competing ions have and what is its reason?

A

overestimation, Too much of the precipitate will form.

87
Q

what effect does weighing the precipitate before it is dry have and what is its reason?

A

overestimation, The water present will increase the apparent mass of the precipitate.

88
Q

what effect does not rinsing the precipitate before drying it have and what is its reason?

A

overestimation, As the precipitate dries, other soluble chemicals will begin to crystallise out of the small amount of solution still trapped in the precipitate. These will add to the mass.*

89
Q

what effect does adding too much of the precipitate-causing chemical have and what is its reason?

A

no effect, This is a necessary part of the method to make sure that all of the required ions are in the precipitate. The chemical must be in excess.

90
Q

what effect does using too much water for the initial dissolving have and what is its reason?

A

no effect, This is a practical consideration — the more water you have, the longer the filtering step.

91
Q

steps for stoichiometry success?

A
  1. Ensure you have a balanced full or ionic (spectator ions removed) equation
  2. List all the specific quantitative information you’re given in the question under the relevant species in the balanced equation. This will allow you to identify your “known” and “unknown” chemicals.
  3. Determine the number of moles of your “known” chemical using either
    n = m/M or n = cV
  4. Use the mole ratio in the balanced equation to find the number of moles of “unknown” chemical using the cross multiple strategy or similar.
  5. Find either the mass or concentration or volume your “unknown” chemical using either
    m = n x M or C = n/V or V = n x VM
92
Q

what can analysis of light be?

A

Analysis can be both qualitative and quantitative.

93
Q

what is Qualitative?

A

non-numerical

94
Q

what is Qualitative used for?

A

Typically used to confirm (or refute) the presence of a contaminant in a water sample

95
Q

what is Quantitative?

A

numerical

96
Q

what is Quantitative used for?

A

Typically used to determine the concentration of a particular contaminant in a water sample.

97
Q

what are the two types of light analysis?

A
  • Colorimetry
  • UV-Vis spectroscopy
98
Q

how many types of light are there?

A

There are different types of light (electromagnetic radiation)

99
Q

what happens with light wavelength and energy?

A

As the wavelength ↑, energy ↓
As the wavelength ↓, energy ↑

100
Q

what do the different light analysis use?

A

Different types of analysis use light of different wavelengths.

101
Q

what does light equal?

A

electromagnetic radiation

102
Q

how can radiation be used for analysis using light?

A
  • Measure the radiation emitted by a sample
  • Measure the radiation absorbed by a sample
103
Q

what is colorimetry?

A

Analysis using visible light

104
Q

what is the colour of chemicals?

A

The colour of chemicals we see around us are a result of how various colours of light interact with the chemical.

105
Q

how can colours be organised?

A

There are 1o colours of light that mix to give 2o colours. Mixing all the colours of the visible spectrum results in white light.
Coloured light can also be organised into pairs of complementary colours.

106
Q

what happens when complementary colours combine?

A

When complementary colours of visible radiation are combined they also appear as white light.

107
Q

how does visual radiation appear white?

A

Visual radiation will therefore appear white if it is either a combination of 2 complementary colours, or a mix of all colours.

108
Q

how are objects coloured?

A

An object that appears a particular coloured, has absorbed the complementary colour and reflects the colour it is.

109
Q

what is calorimetry?

A

instrumental analysis (Calorimetry is the process of measuring the amount of heat released or absorbed during a chemical reaction)

110
Q

what are the requirements for colorimetry?

A
  • Sample must be coloured (contains transition metal).
  • Generally used for quantitative analysis (finding conc.), rather than qualitative analysis.
  • What’s in the sample already known, a wavelength of visible radiation that is known to be absorbed is selected.
111
Q

what is the process for colorimetry practical?

A
  1. Selected wavelength of visible radiation (could use colour filter with lamp to make correct colour)
  2. known amount passes through sample
  3. Amount of absorption detected by detector and is compared to known standards on a calibration curve to determine exact concentration.
112
Q

what does colorimetry require?

A

Colorimetry required a calibration curve to be created.

113
Q

what does a calibration curve entail?

A

This involves making 4 - 5 standard solutions of the coloured chemical you are analysing your water sample for.

114
Q

what does the calibration curve establish?

A

The calibration curve establishes a relationship between conc. of contaminant and absorption. Only then can your water sample be compared, and its concentration determined.

115
Q

colorimetry steps?

A
  1. Prepare a set of standards of known concentration.
  2. Measure the amount of light absorbed by each standard.
  3. Plot a calibration curve (standard curve).
  4. Determine the concentration of the sample from the calibration curve.
116
Q

what are advantages of colorimetry?

A
  • Relatively cheap
  • Samples do not need to be pure for analysis to be done, just smart selection of wavelength of light.
117
Q

what is UV-Vis spectroscopy?

A

Analysis using ultraviolet light

118
Q

characteristics of UV-Vis spectroscopy?

A
  • Works on the same principle as colorimetry except UV radiation is used.
  • Sample may be coloured or colourless as long as ultraviolet radiation can be absorbed.
119
Q

what is the process for uv-vis spectroscopy?

A
  1. Selected wavelength of UV radiation
  2. passes through sample may use mirrors and reference/blank to determine if solvent absorbs.
  3. Amount of absorption detected by detector and is compared to known standards on a calibration curve to determine exact concentration.
120
Q

How do we collect water for testing?

A

There are a variety of analytical techniques that can be carried out on water, some cheap and simple, others complex, expensive and involving instruments.

121
Q

what must happen to water prior testing?

A

Prior to testing, water must first be collected from its source (creek, sea, drinking supply) using the correct water sampling protocols.

122
Q

Key water sampling protocols include?

A

Representative sampling
- Variety of locations or depths at the relevant water source
- Collected at “average conditions”

Sampling equipment and procedures
- Avoid contamination from person taking sample + sample containers + during transportation
- Duplicate samples

123
Q

define Salinity

A

Salinity is a measure of the amount of salt (of any type) in water.

124
Q

what does salinity determine?

A

Salinity determines if water is drinkable, what aquatic life can survive in it, and in what industries it can be used in.

125
Q

how can salts conduct electricity?

A

Since salts contain charged particles (ions), when they are dissolved in water, this charge is free to move, and the water is able to conduct electricity.

126
Q

what can Concentration and conductivity can be measured in?

A

Concentration and conductivity can be measured in a range of different units.

127
Q

what is the relationship between salt and electrical conductivity?

A

This means that greater the amount of salt, the higher the electrical conductivity of the water will be.

128
Q

how can we test salinity levels?

A

In order to test the salinity levels of a water sample (eg from a creek), a calibration curve must first be created.

129
Q

what is a calibration curve for salinity?

A

This is made be making up 4 - 7 standard solutions with accurately known salt concentration and testing each of their levels of electrical conductivity. These values are then recorded graphically (calibration curve).

130
Q

what happens with water testing after the calibration curve is formed?

A

Then, the water sample under investigation (eg creek water) can be analysed. Its electrical conductivity is tested and recorded in the same way as the standard solutions were.

131
Q

how can salinity finally be determined form a water source?

A

This conductivity is then found on the calibration curve and the corresponding concentration read off the graph. This is then determined to be the concentration of salt/salinity in that water sample.

132
Q

challenge of testing water salinity with electrical conductivity?

A

all salts conduct, not just NaCl

133
Q

define Excess reagent

A

the reactant that we have too much of, according to the stoichiometric mole ratio in the balanced equation. Some of this reactant will be unreacted (left over) at the end of the reaction

134
Q

define Limiting reagent

A

the reactant will completely react, according to the stoichiometric mole ratio. None of this reactant will be unreacted (left over) at the end of the reaction. This reactant should always be the one used when doing stoichiometry calculations to determine the amount of product formed.

135
Q

what is a titration?

A

A titration is used to accurately determine the conc. of one solution, when you already know the conc. of another solution (quantitative analysis).

136
Q

what is a titration sometimes referred to as?

A

A titration is sometimes referred to as volumetric analysis as the data collected is a volume.

137
Q

what do you do in a titration?

A

In a titration you react a known volume of one solution (measured in a pipette) with a known volume of another solution (measured in a burette). You can tell when the reaction is complete because
* either an indicator which has been added changes colour, or
* one of the solutions itself changes colour.

138
Q

safety in titrations?

A
  • follow instructions precisely
  • wear safety glasses
  • acids and alkalis are corrosive: handle them carefully and mop up any spills
139
Q

steps of titration?

A
  1. Label and fill two beakers with the reacting solutions.
  2. Pour a little of one solution into the burette to rinse it. Check the tap works. Pour away all this solution.
  3. Fill the burette.
    Run liquid through the tap until there are no air bubbles. Zero the burette.
  4. Using a pipette filler, rinse out the pipette with the other solution. Then refill the pipette to well above the mark.
  5. Carefully let the solution out until the meniscus is on the line.
  6. Run this solution into a conical flask. Do not force out the last drop, but just touch the pipette tip on the liquid surface.
  7. Add just enough indicator to produce a
    definite colour (about
    2-5 drops). Put the conical flask on a white tile. Adjust the height of the burette so that it just sticks into the neck of the conical flask.
  8. Run solution from the burette into the conical flask, swirling the flask all the time. Do not shake the flask, or solution will get splashed up the sides where it may not react.
  9. Stop when the indicator changes colour and note the volume run in from the burette.
  10. Empty and rinse the conical flask. It need not be dried, because any water will dilute both solutions equally.
  11. Refill and re-zero the burette.
  12. Using the pipette filler, refill the pipette and zero it.
  13. Repeat steps 5, 6, and 7.
  14. Repeat step 8 but this time stop about
    1 cm before the previously recorded volume. Then add the solution drop by drop until the colour just changes.
  15. Record the volume added in a table
  16. Do at least two accurate titrations and work out the average volume added.
140
Q

how much does a burette typically hold?

A

One of your solutions will be in the burette. Burettes typically fit up to 50mL of solution.

141
Q

what is a burette used for?

A

Burette is used to determine the titre for the practical. It is a measure of the volume of solution needed to “neutralise” the solution already in the conical flask (in an acid/base titration).

142
Q

what is a titre?

A

Titre (mL) = final volume (mL) - initial volume (mL)

143
Q

Using a burette key tips?

A
  • Do not waste time getting burette to exactly 0mL
  • Make sure solution is within the 50mL reading range (not above)
  • Tip of burette must be filled prior to reading any measurements
  • Read measurements at the bottom of the meniscus
  • Avoid parallax error
144
Q

what is an end point and how is it observed?

A

A colour change is used to indicate the end point of the titration (when to stop adding solution from the burette). The end point is often triggered by an indicator added to the conical flask (in an acid/base titration).

145
Q

what is the indicator aim?

A

The aim is to select an indicator that gives an end point as close as possible to the equivalence point.

146
Q

what is the Equivalence point?

A

The equivalence point is when the correct mole ratio between the reactants has been achieved in the conical flask (according to the relevant balance equation). For many acid/base titrations this will occur at pH=7 but it does not have to (depending on if strong/weak acids/bases are used).

147
Q

how do you select an indicator?

A
  • Depending on the acid/base combination used the pH at equivalence may or may not be pH=7.
  • The experimenter must know the pH at equivalence before the titration is carried out so the correct indicator can be used. This helps ensure an end point as close as possible to the equivalence point will occur in the practical.
148
Q

how long does titration go for?

A

The titration practical is repeated until concordant titres are achieved. This is 3 x titres that are all within a 0.1mL range.

149
Q

what does concordant titres mean?

A

Achieving concordant titres indicates precise (tightly grouped results) and suggests repeatable results. This is desirable in any form of analysis.

150
Q

what are the concordant titres used for?

A

The concordant titres are then used to determine the average titre which is used in subsequent calculations.

151
Q

Washing glassware for titration?

A

It is critical that all glassware gets washed correctly.

Burette - double wash
1. With distilled water
2. With solution to go into it

Pipette - double wash
1. With distilled water
2. With solution to go into it

Volumetric and conical flask - single wash
1. With distilled water

152
Q

what is Volumetric analysis?

A

To determine the concentration of one solution, using the accurately known concentration of another solution.

153
Q

Simple titration calculations steps?

A
  1. Use given conc and volume to find moles for known n=CxV
  2. Use mole ratio to move between moles of known and moles of unknown
  3. Find conc of unknown, using given volume, by C=n/V

NB: Slight variations on these steps are possible, eg C=m/V, n=m/M, %, dilution

154
Q

what are pH at equivalence?

A

Not all salt and water combinations are in fact neutral

155
Q

how to determine pH of strong acid and base at equivalence?

A

No ions present in the salt will impact the pH at the equivalence point
∴ for a strong acid with strong base, pH at equivalence will always be pH = 7

156
Q

what indicator is used for strong acid and base reactions?

A

Phenolphthalein indicator is often used to determine the end point of these titrations

157
Q

how to determine pH of weak acid or base at equivalence?

A

Consider whether the ions in the salt can do a second acid or base reaction with water? and if there is more OH- or H3O+, this will determine pH.

158
Q

errors in titrations?

A
  • Rinsing water left in the burette
  • Rinsing water left in the pipette
  • Rinsing water left in volumetric flask when making a standard
  • Rinsing water left in conical flask
  • Water used to rinse down sides of conical flask during titration
159
Q

impact of error in titrations of Rinsing water left in the burette?

A

→ this dilutes the solution in the burette
(↓ its conc.)

160
Q

impact of error in titrations of Rinsing water left in the burette - If your unknown is in the burette?

A

Titre volume will ↑ (greater volume to get to equivalence point)
→ underestimate of unknown’s true conc.

161
Q

impact of error in titrations of Rinsing water left in the burette - If your unknown is in the conical flask/pipette?

A

Titre volume will ↑ (greater volume to get to equivalence point)
→ overestimate of unknown’s true conc.
(unknown appears more conc than it is)

162
Q

impact of error in titrations of Rinsing water left in the pipette?

A

→ this dilutes the solution in the pipette
(↓ its conc.)

163
Q

impact of error in titrations of Rinsing water left in the pipette - If your unknown is in the burette?

A

Titre volume will ↓ (smaller volume to get to equivalence point)
→ overestimate of unknown’s true conc.
(unknown appears more conc than it is)

164
Q

impact of error in titrations of Rinsing water left in the pipette - If your unknown is in the conical flask/pipette?

A

Titre volume will ↓ (smaller volume to get to equivalence point)
→ underestimate of unknown’s true conc.

165
Q

impact of error in titrations of Rinsing water left in volumetric flask when making a standard?

A

→ no effect

166
Q

impact of error in titrations of Rinsing water left in conical flask?

A

→ no effect

167
Q

impact of error in titrations of Water used to rinse down sides of conical flask during titration?

A

→ no effect

168
Q

The difference in concentration between two solutions can be communicated in a range of ways?

A
  • its colour (if solute is coloured)
  • its numerical concentration (in molL-1, gL-1 etc)
  • visualising the solute/dissolved particles and their spacing/density
169
Q

what is A ‘stock’ solution?

A

A ‘stock’ solution is a general term used to describe an original solution (whose concentration is often high) that is going to be used to create a diluted version of the solution.

170
Q

what will the diluted solution from stock solution contain?

A

The diluted solution will contain a certain volume of stock solution + some volume of water to give a new total volume.

171
Q

Compare a stock and diluted solution: What’s the same?

A
  • Mass (m) of solute
  • Moles (n) of solute
172
Q

Compare a stock and diluted solution: What’s different?

A
  • Volume (V) of solution
  • Conc (molL-1/gL-1) of solution
173
Q

Finding conc. of diluted solution?

A
  1. Identify Conc and Volume of the stock solution. Label as C1 and V1.
  2. Identify Volume of diluted solution. Label as V2.
  3. Use C1V1 = C2V2 to solve for C2

Chemistry Unit 2 (5 decks)

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