Amount of substance

Question 1

What is the Avogrado’s constant?

Answer 1

It tells us how many particles are in one mole of a substance.

Question 2

How do you calculate the mass of a substance using Mr and the number of moles?

Question 3

How do you calculate the number of moles using concentration and volume?

Question 4

What is the ideal gas equation?

Question 5

How do you go from cm3 to m3?

Answer 5

x 10 to the power of 6

Question 6

Write the ionic equation for the reaction of nitric acid and sodium hydroxide.

Question 7

How do you calculate gas volumes?

Answer 7

number of moles= volume/ 24

Question 8

How do you make a standard solution for titration?

Answer 8

1. Weight out the required mass of the solid using a top-pan balance.
2. Make sure to reweigh it once you have added it to the beaker so you know the exact amount of solid used.
3. Add distilled water to the beaker and stir to make sure the solid has dissolved.
4. Pour the solution into a 250 cm3 volumetric flask and top it up to the line with distilled water.
5. Make sure the bottom of the meniscus touches the line.
6. Shake the volumetric flask to make sure the solution is uniform.

Question 9

Describe how you would carry out a titration.

Answer 9

1. Use a pipette to measure out 25 cm3 of the alkali and place it in the flask.
2. Then fill up the burette with acid with the bottom of the meniscus touching the line.
3. Use a funnel to pour the acid in and then remove the funnel when all the acid is in.
4. Add an indicator of the acid.
5. First do a rough titration to get an idea of where the endpoint is.
6. Then keep doing titrations and add the acid dropwise and you get close to the endpoint.
7. Do this until you get concordant results.

Question 10

What are concordant results?

Answer 10

Results that are 0.1 cm3 from each other.

Question 11

Why should you remove the funnel after you have done the titration?

Answer 11

To make sure that no acid drips into the burette and affects the titre results.

Question 12

What is an empirical formula?

Question 13

What is a molecular formula?

Question 14

A molecule has an empirical formula of C4H3O2 and an MR of 166. Find the molecular formula.

Question 15

How do you calculate percentage yield?

Question 16

Why might a reaction not have a 100% percentage yield?

Answer 16

Not all the reactants react fully or in the expected way. Some chemicals are lost to the environment.

Question 17

How do you calculate atom economy?

Question 18

What is atom economy?

Answer 18

The proportion of the reactants that became part of the desired product.

Question 19

What are the economic advantages of having a high atom economy?

Answer 19

1. There will be less waste which means less money will be wasted.
2. There will be less waste meaning that the company will spend less money on separating the waste from the desired product and disposing of it safely.

Question 20

What are the environmental advantages of having a high atom economy?

Answer 20

1. Less waste chemicals which are harmful to the environment will be produced.
2. Less non-renewable resources will need to be used to make a desired amount of a certain product.