Mod 6 Quantitative Analysis Flashcards

Question

What is the formula for KHP? Is it used as a primary standard?

Answer 1

It is used as a primary standard. Has the formula: KH (C8H4O4)

Answer 2

Using the example of sodium carbonate: Calculate th required mass of anhydrous Na2CO3, weigh out the required mass of dried Na2CO3 into a clean, dry beaker, record the exactt mass weighed out. Dissolve the solid in distilled water using a stirring rod. Rinse a 250mL volumetric flask with distilled water. Transfer the dissolved Na2CO3 into the 250mL flask, and fill the flask up to the line, Make sure the meniscus is on the mark. May want to use a Pasteur Pipette for the last few drops . Stopper the flask and shake/invert it 10-20 times to mix thoroughly

Answer 3

Rinse a burette and clamp it onto a retort stand. Fill burette with either titrant or titrand with a plastic funnel. Ensure no air bubbles in the burette. Rinse pipette with distilled water and then fill the pipette until the mark with either the analyte or standard solution (whicever is in the conical flask) Transfer aliquot into the conical flask by resting the tip of pipette against the inner glass, and allowing it to drain under gravity. DONT attempt to completely drain the residual slution Add 3 drops of a suitable indicator. Position conical under burette tip, and open the tap, and run it into it to continue swirling until the indicator just changes colour. Record final burette reading to 2dp Titre = final - initial burette reading

Answer 4

Occurs when the acid/base has stoichiometrically reacted with the base/acid

Answer 5

Ka = ([H3O+][A-]) / [HA]

Answer 6

Kb = ([OH-][BH+]) / [B]

Answer 7

Kw = [H+][OH-] = 10^-14 But the general idea is when H+ = OH-

Answer 8

Kw = Ka * Kb

Answer 9

A solution that tends to resist any great change in pH when small quantities of acid or base are added to it

Answer 10

A weak acid and a salt of that weak acid (conjugate base) OR A weak base and a salt of that weak base (conjugate acid)

Answer 11

More ; it results in less change in pH

Answer 12

HA (aq) + H2O (l) ⇌ H3O+ (aq) + A− (aq) If an acid is added to the buffer solution, this increases [H+] and consequently the [H3O+] to the buffer solution. The equilibrium will shift to the left as the conjugate base A- combines the added H3O+ to form HA in order to minimise the increase in [H+], according to LCP If a base is added to th solution, this increases [OH-], and would react out the H3O+ and cause the equilibrium to shift to the right to minimise the loss of H3O+, according to LCP. HA will ionise to produce more A- Thus because of its ability to maintain an approximately constant pH, such a solution is called a buffer solution: it acts as a ‘buffer’ against change in pH.

Answer 13

B (aq) + H2O (l) ⇌ BH+ (aq) + OH− (aq) If an acid is added to the buffer solution, hydrogen ions (H+) are added to the buffer solution above, the added H+ will react with the OH- in the buffer solution, removing OH- from the buffer equilibrium. The equilibrium will then shift to the right to favour the forward reaction to produce more OH- and minimise the disturbance caused according to LCP If a base is added to the buffer solution, the [OH-] increases in the buffer solution above, causing the equilibrium to shift to the left to use the excess OH−, according to Le Chatelier’s Principle. Thus because of its ability to maintain an approximately constant pH, such a solution is called a buffer solution: it acts as a ‘buffer’ against change in pH.

Answer 14

The carbonic acid - bicarbonate buffer exists in natural systems such as human blood to adjust for any fluctuating pH changes outisde of 7.35 - 7.45

Answer 15

As cells in our bodies produce the carbon dioxide as a form of waste, it dissolves in blood forming carbonic acid, through the following equilibrium system CO2 (g) + H2O (l) ⇌ H2CO3 (aq) The carbonic acid is an unstable and weak acid, which dissociates to form the hydronium ion and bicarbonate polyatomic ion (HCO3-) H2CO3 (aq) + H2O (l) ⇌ HCO3− (aq) + H3O+ (aq) (IMPORTANT TO RMBR) When there is an acid increase H+, the equilibrium shifts to the left (favours the reverse reaction) forming carbonic acid (H2CO3) molecules. For example, a common way the pH of blood can decrease is due to the presence of lactic acid (C3H6O3). Lactic acid is produced in muscle cells when oxygen levels in the body is low When there is an increase in bicarbonate (HCO3 −) in the blood, as bicarbonate is another cellular waste product from metabolism, the buffer system reacts to the presence of extra bicarbonate in the blood and causes a shift to the left of the equilibrium system (favours the reverse reaction).

Answer 16

Neutralising spills. Large quantities of hazardous acids and bases are commonly used in industrial processes. In the event of a spill, acid or base must be neutralised and contained to minimise damage and risk of injury Neutralisations are exothermic, and can give off lots of heat, thus a weak amphiprotic species such as sodium bicarbonate (NaHCO3) is used for neutralising strong acids and bases

Answer 17

They have used their technique of using acids and bases through their choice of selecting specific fruits and plants to meet their specific needs. By performing volumetric analysis such as titration, chemists are able to determine the nature and concentration of various substances (acids and bases) that are contained within the fruits and plants used by Aboriginal and Torres Strait Islander Peoples. The Davidson plum is a natural Australian fruit that approximately 100 times more ascorbic acid (vitamin C) than contained in an orange. For such reason, it has a very sour taste due to the high concentration of acid. Aboriginal and Torres Strait Islander Peoples consumed the Davidson plum as way to boost their body’s nutrient level which reduced their chance of having scurvy disease. When exposed to water, the Soap Tree’s leaves is able to lather or produce a soap solution that have antibacterial properties and thus act as an antiseptic. The reason for this is that the leaves contain saponin acid which has the ability to suppress bacteria growth. Aboriginal and Torres Strait Islander Peoples used the soap tree leaves as a way to heal cuts on their skin Aboriginal and Torres Strait Islander Peoples also used yellow ochre (hydrated iron hydroxide, Fe(OH)3) to treat stomach upsets. The chemistry behind is that the yellow ochre is basic and thus can react and neutralise with any excess hydrochloric acid in the stomach. This served as a way for Aboriginal and Torres Strait Islander People to remove any heartburns or stomach upsets. The yellow ochre has base similar to antacids which is an example of medicine used in everyday life. Mangroves are used to treat stingray injury by preventing infection and neutralise the mildly acidic stingray venom. This is done by smashing the Grey Mangroves’s leaves and adding water to create a mixture that is a base which can be applied to the wound caused by the stingray.

Answer 18

Concentration of the ions it contains Number of charges carried by each ion Mobilities of these ions ( i.e, a massive ion such as acetate will have low mobility, leading to a low conductivity) Note: a neutral molecule will carry very little conductivity (H2O is uncharged)

Answer 19

H+ = 34.98 --> OH- = 19.80 Typically cations have a higher conductance than the anions

Answer 20

Misreading numbers on scale Mistakenly using a pipette of incorrect volume Spilling a portion of the sample Incorrect rinsing of volumetric glassware Use of wrong standard solution (i.e. hygroscopic NaOH over H2CO3)

Answer 21

A faulty balance Inaccurately calibrated pipette Use of an unsuitable indicator Reading the scale on a burette with a constant parallax error

Answer 22

Should have an equivalence point that occurs at pH 7, step change occurs between pH of 4 and 10. Therefore, an indicator has to lie in that range. Thus, we can use Phenolphthalein, Bromothymol blue and methyl orange

Answer 23

Phenolphthalein, Bromothymol blue and methyl orange

Answer 24

Has equivalence point occurring above pH 7. Step change in pH occurs between pH 7 and pH 11. Thus, phenolphthalein is the best option

Answer 25

Equivalence point below pH 7. Step change in pH occurs between 3 and 7. Thus, methyl orange is the best option