quantitative chemistry

Question 1

What is conservation of mass?

Answer 1

The total mass of the products is equal to the total mass of the reactants.

Question 2

What can a half equation be used to show?

Answer 2

It can be used to show what happens to one reactant in a chemical reaction with electrons written as e-.

Question 3

2 half equations for iron and copper(II) sulfate

Answer 3

Cu2+ (aq)+ 2e- → Cu(s)
Fe(s) → Fe 2+ (aq)+ 2e-.

Question 4

What are the spectator ions?

Answer 4

The ions that are not involved in the reaction.

Question 5

What is the relative formula mass?

Answer 5

The relative formula mass of a compound is the sum of the relative atomic masses of all the atoms in the numbers shown in the formula.

Question 6

How can some reactions appear to have a change in mass?

Answer 6

By the reaction being carried out in a non-closed system and include a gas that can enter or leave.

Question 7

What is a mole (mol)?

Answer 7

A mole is a measure of the number of particles (atoms, ions or molecules) contained in a substance.

Question 8

What is Avogadro constant?

Answer 8

6.02 * 1023

Question 9

What is the equation for the amount of substance in a given mass?

Answer 9

Amount (mol)=mass of substance (g) /
atomic (or formula) mass (g/mol)

Question 10

What is a limiting reactant?

Answer 10

When one chemical is used up, it stops the reaction going any further. It is called the limiting reactant. The other chemical which isn’t used up is known as the excess.

Question 11

What is the equation for volume?

Answer 11

Volume=amount (mol)* 24dm3

Question 12

What is concentration often measured in?

Answer 12

The concentration of a solution= amount of substance (mol)
volume (dm3)

Question 13

What is titration?

Answer 13

Titration is an accurate technique that can be used to find out how much of an acid is needed to neutralise an alkali.

Question 14

Determination of the reacting volumes of solutions of a strong acid and a strong alkali by titration. (RP)

Answer 14

1) Wash and rinse a pipette with the alkali being used.
2) Use the pipette to measure out a known and accurate volume of alkali.
3) Place the alkali in a conical flask.
4) Add a suitable indicator eg phenolphthalein.
5) Place the flask on a white tile so the colour can be seen clearly.
6) Place the acid in a burette.
7) Take the initial reading.
8) Carefully add the acid to the alkali swirling the flask to mix.
9) Continue until you see a colour change.
10) Take the final reading.
11) Calculate the volume of acid added.

Question 15

What is yield?

Answer 15

The amount of product obtained.

Question 16

How do you calculate percentage yield?

Answer 16

Percentage yield = yield from reaction
*100
maximum theoretical yield

Question 17

What is atom economy?

Answer 17

It is a measure of the amount of reactant that ends up in a useful product.

Question 18

What is the equation for atom economy?

Answer 18

Atom economy= relative formula mass of the desired product/ sum of the relative formula mass of all the reactants * 100

Question 19

How is ethanol produced?

Answer 19

Produced by hydration and fermentation.
During hydration, ethene is reacted with steam to form ethanol:
C2H4 + H2O = C2H5OH
Atom economy for hydration is 100%.
Hydration of ethene is an addition reaction- all reactant atoms end up in a desired product.
Ethanol can also be produced by fermentation:
C6H12O6 = 2C2H5OH +2CO2
-Only half of the atoms in the reactants end up in a desired product.

Question 20

What are the important factors when choosing a reaction pathway?

Answer 20

-The atom economy.
-Cost of reactants.
-The percentage yield
-The usefulness of by-product’s.

Question 21

Tips on how to answer mass question.

Answer 21

1) Write down the right equation.
2) Write what the question gives you in the equation.
3) Look at the units.
4) Molar ratio.
5) Input values again.

Question 22

Ca(OH)2 + H2SO4 → CaSO4 + 2H20.
0200 mold-3 and 300cm3 of Ca(OH)2 reacts with H2SO4 to form CaSo4. Find the mass of CaSO4vand H20 needed.

Answer 22

1) use the right equation. Mol=mass/mr and Mol=Conc * vol.
2) Substitute the values in. 300/1000 * 0.200=0.06
3) Check the molar ratio and find the mass. CaSO4= 0.06* 136.2=8.172g. 2H2O=0.06 * 2 (to get the molar ratio)=0.12*18=2.16g