C4: Quantative Chemistry Flashcards
What is Mr?
Relative formula mass has the symbol, Mr. To calculate the Mr for a substance: work out how many atoms of each element there are in the chemical formula.
What is the equation for moles in terms of m and mr?
N = m/mr
What is the equation for moles in terms of volume and concentration?
N = c x v
What is concentration measured in?
Mol/ dm^3
What is volume measured in?
dm^3
What is mass measured in?
Grams
What is giga in metres?
10^9 m
What is mega in metres?
10^6 m
What is kilo in metres?
10^3 m
What is deci in metres?
10^-1 m
What is centi in metres?
10^-2
What is milli in metres?
10^-3 m
What is micro in metres?
10^-6 m
What is nano in metres?
10^-9m
What is the effect of a limiting reactant on the amount of product made?
Mass is measured in kilograms (kg) or grams (g). of product formed in a reaction depends upon the mass of the limiting reactant. This is because no more product can form when the limiting reactant is all used up.
how do you identify the limiting reactant in a chemical reaction?
To find the limiting reactant, you need to determine the number of moles of each reactant that is present in the reaction. Then, you need to calculate the number of moles of product that could be produced from each reactant using the molar ratio. The reactant that has a lower actual mol than theoretical mol is the limiting reactant.
What is theoretical yield?
The highest potential product formed in a reaction
What is the actual yield?
Actual yield is the actual mass of product formed through inneficiency
What are reasons for inefficiency, causing a reduced product?
- Not all limiting reactant is used up
- Product escaping the reaction vessel
- Physical loss of product during transfer
- Reactants may act in different ways to the expected reaction
How do you calculate percentage yield?
(Actual yield/ Theoretical yield) x100
What is atom economy?
The amount of useful product as a percentage of total product formed. A measure of the amount of starting materials that end up as useful products
Reactant A + Reactant B = Product + Waste
How do you calculate atom economy?
(Formula Mass of desired product/ Formula Mass of total product including waste) x 100
Why can percentage yield never be above 100%?
The yield in a chemical reaction cannot exceed 100% because of the Law of Conservation of Mass, which states that matter is neither created nor destroyed. Therefore, the total mass of reactants must equal the total mass of products.
How can concentration of a solution be changed?
Often, a worker will need to change the concentration of a solution by changing the amount of solvent. Dilution is the addition of solvent, which decreases the concentration of the solute in the solution. Concentration is the removal of solvent, which increases the concentration of the solute in the solution
How do you convert between grams and dm^3
g/1000 = dm^3
m/1000= v
how do you calculate amount of solute using conc of solution?
Amount of solute =C in amount of solute volume of solution ×V in volume of solution
How do you calculate the titre volume?
The volume of acid added is the final volume minus the start volume. To find the average titre (titration volume) the concordant values (often within 0.05cm^3 of each other) are added together and divided by the number of readings that were taken.
What are two indicators commonly used in titration?
Phenolphthalein
Methyl orange
What colour does phenolphthalein turn in acid?
Colourless
What colour does phenolphthalein turn in a base?
Pink
What colour does methyl orange turn in base?
Orange
What colour does methyl orange turn in acid?
Pink
What are soluble salts?
SLAPN salts:
Sodium
Lithium
Ammonium
Potassium
Nitrate
What does as an acid and metal produce?
Acid + metal > Salt + hydrogen
What does an acid and and alkali/ base produce?
Salt + Water
What does an acid and a metal carbonate produce?
Salt + Water + Carbon Dioxide
what does a metal hydroxide and acid make?
Salt + Water
What is an example of a metal hydroxide?
NaOH
What type of pipette is used in titration and what are they used for?
Volumetric pipettes are often used in titrations to measure 25cm^3 of the unknown solution (unknown concentration)
How is the Ar of an isotope calculated?
(Mass number of isotope 1 x Abundance (% in decimal)) + (Mass number of Isotope 2 x abundance (% in decimal))
What is the method for titration?
1) A safety pipette filler should be used to draw up the solution until the bottom of the meniscus is on the line to measure out a fixed volume of the unknown solution and carefully transfer into a conical flask
2) Fill a burette with a dilute acid of known concentration using a funnel, making sure the meniscus is on zero and that the tap is flushed out multiple times with a little of the solution so there are no air bubbles. Make sure you then turn the tap upwards.
4) Add a few drops of indicator into the flask and put the flask onto a white tile under the burette, held up with a retort stand and burette clamp
5) Gradually release the solution in the burette by turning the tap right. One the solution has changed in colour, stop the tap and measure the amount of solution used from bottom of the meniscus
6) Repeat the experiment until you have 2 or 3 concordant results
What are potential errors in reading pipette and burette values?
You must be at eye level with the bottom of the meniscus (curved surface of liquid) to read the burette. Reading from above or below the meniscus will result in a parallax error. In order to better read the meniscus, keep a dark piece of paper behind the buret.
How can you improve the accuracy of a titration?
- Repeat the experiment until you have over 3 concordant results to use for the titre (volume)
- Use a black sheet of paper/ background to accurately measure the volume at the bottom of the meniscus
- Immediately stop the flow of the known solution as the solution changes colour
- Rinse burette several times with distilled water or a little of the solution to prevent air bubbles and thus sustain an accurate volume
What is the use of an indicator in an acid- base titration?
The role of indicator is to mostly find out the point of equivalence when two particular solutions have reached the point of neutralization.
How to convert concentratiom from g/dm^3 to mol/dm^3
Divide by Mr
What substances are bases?
Metal oxides
Metal carbonates
What substances are alkalis?
Ammonia
Metal hydroxide
What is the measurement of a mole?
6.022x10^23
How do you calculate how many atoms of Hydrogen there are in 1 mole H2O
2 x 6.022x10^23 = 1.2044 x 10^24
What volume will 1 mol of gas occupy in room temperature and pressure?
24dm^3
What is the molar gas volume?
24dm^3/mol
Or
24000cm^3/mol
How do you calculate moles in gases at room temp and pressure?
n = v(dm^3)/ 24
Or
n = v(cm^3)/ 24000
How does temp affect volume of gas?
As temp increases, volume increases. The particles gain kinetic energy and move faster. They collide more often with greater force on the container walls. Since the container can expand, the gas volume increases until the pressure of the gas is back to the constant atmospheric pressure.
How does pressure affect volume of gas?
As gas volume increases, pressure decrease
Inversely proportional
What is an isotope?
Isotopes are distinct nuclear species of the same chemical element. They have the same atomic number and position in the periodic table, but different nucleon numbers due to different numbers of neutrons in their nuclei.
What is the equation for finding empirical formula?
n= %/mr
Or
n= m/mr
Then divide by the smallest mol of each atom
What is the formula of ammonia?
NH3
What is the formula for ammonium?
NH4
