3. Quantitative Chemistry

Question 1

How can you calculate the percentage mass of an element in a compound?

Answer 1

((Aᵣ x number of atoms of that element) / Mᵣ of the compound) x100.

Question 2

What is one mole of any substance?

Answer 2

The amount of that substance that contains an avagadro number of particles (6.02x10²³).

Question 3

How do you calculate number of moles?

Answer 3

mass in g/Mᵣ.

Question 4

What is conservation of mass?

Answer 4

No atoms are created or destroyed. Same types and number of atoms on either sides of a reaction equation.

Question 5

What are two explanations for observing a change in mass of an unsealed reaction vessel?

Answer 5

1. MASS INCREASE:
   - one of the reactants is a gas that’s found in the air and all the products are solds, liquids or aqueous.
   - the gas reacts to form part of the product and becomes contained inside the vessel.
2. MASS DECREASE:
   - because one of the products is a gas.
   - the gas can escape as the vessel isn’t closed.

Question 6

What is a limiting reaction?

Answer 6

The reactant that is used up in a reaction.

Question 7

The amount of product formed is ________ to the limiting reactant? Why?

Answer 7

Directly proportional. The more reactant, the more reactant particles so the more product particles.

Question 8

How do you calculate the volume of a gas?

Answer 8

(mass of gass/Mᵣ of gas)x24 (at room temperature (20) and pressure).

Question 9

What is concentration?

Answer 9

The amount of a sunstance in a certain of volume of solution. The more solute in a given volume, the more concentrated the solution is.

Question 10

How do you calculate concentration (g/dm³)?

Answer 10

mass of solute/volume of solvent.

Question 11

How do you calculate concentration (mol/dm³)?

Answer 11

number of moles of solute/volume of solvent.

Question 12

What is atom economy?

Answer 12

Tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as useful products.

Question 13

What is the equation of atom economy?

Answer 13

(relative formula mass of desired products/relative formula mass of all reactants)x100.

Question 14

Why is a low atom economy bad?

Answer 14

• use up resources quickly.
• make a lot of waste materials that have to be disposed of somehow (unsustainable).
• aren’t usually profitable (raw materials expensive to buy and waste products are expensive to dispose of responsibly).

instead can find a use for the waste products.

Question 15

Which reactions will have an atom aconomy of 100%?

Answer 15

Ones that only have one product.

Question 16

What is yeild?

Answer 16

The amount of product you get.

Question 17

How do you calculate percentage yeild?

Answer 17

(mass of product actually made/ maximum theoretical mass of product) x100.

Question 18

What does 100% yeild mean?

Answer 18

You got all the product you expected to get.

Question 19

What does 0% yeild mean?

Answer 19

No product was made.

Question 20

Why should industrial processes have a high percentage yeild?

Answer 20

To reduce waste and cost.

Question 21

What are three common problems which result in less than 100% yeild?

Answer 21

1. Reversible reactions.
2. Might be side reactions.
3. You lose some product when you seperate it from the reaction mixture.