Chapter 3 - How Much?

Question 1

Why do we count only protons and neutrons to calculate the mass number of an atom

Answer 1

The mass f an electron is very small compared with a proton or neutron and so the mass of an atom is made up almost entirely of its protons and neutrons.

Question 2

What is the mass number

Answer 2

The total number of protons and neutrons in an atom

Question 3

The number of protons and ___in an atom must always be the same, but there can be different number of ___

Answer 3

1) ELECTRONS

2) NEUTRONS

Question 4

What are atoms of the same element but with different numbers of neutrons called

Answer 4

Isotopes

Question 5

What is mole

Answer 5

The relative atomic mass of an element in grams

Question 6

How do you find the relative formula mass (mr)

Calculate mr of calcium chloride:
CaCl2

Answer 6

Add up all the relative atomic masses of the atoms in its formula

Ar of Ca=40
Ar of Cl=35.5
So mr=40+35.5+35.5
=111

Question 7

If it asks u what the mass of one mole of a substance is, what units do u use

Answer 7

Grams (g)

Question 8

To find the percentage of an element in a compound, what do you do

What is the percentage of carbon in carbon dioxide, CO2

Answer 8

Find the relative formula mass and then divide the relative atomic mass of the element by the total of the relative formula mass and multiply by 100

Ar of C= 12, Ar of O=16
Mr of CO2=12+16+16 =44
(12/44)x100=27.3%

Question 9

What is the link between protons and neutrons mass

Answer 9

They have the same mass and so the relative masses of a proton and a neutron are both one (1)

Question 10

SEARCH HOW TO DO MOLES IN CHEMISTRY BOOK

Question 11

What does yield mean

Answer 11

How much you make

Question 12

How do you calculate the percentage yield

Answer 12

Amount of product made/maximum amount of product possible x 100

Question 13

Why is it not usually possible to get 100% yield from a chemical reaction

Answer 13

Reactions may not go to completion, other reactions may happen and some products may be lost when it is separated or collected from the apparatus.

Question 14

What are the advantages of using reactions with high yields in industry

Answer 14

It helps to conserve resources and to reduce waste. Working in the ways helps to reduce pollution and makes production more sustainable

Question 15

What is a reversible reaction

Answer 15

The products of the reaction can react to make the original reactants

Question 16

What are food additives

Answer 16

Substances added to food to improve its qualities. They can be natural products or synthetic chemicals

Question 17

What methods can be used to ensure only safe, permitted additives have been used

Answer 17

Paper chromatography and mass spectrometry

Question 18

How is paper chromatography used to analyse the artificial colours in food

Answer 18

A spot of colour is put onto paper and a solvent is allowed to move through the paper. The colours move different distances depending on their solubility.

Question 19

How does gas chromatography work

Answer 19

The mixture is carried by a gas through a long column packed with particles of a solid. The individual compounds travel at different speeds through the column and come out at different times. The amount of substance leaving the column at different times is recorded against time and shows the number of compounds in the mixture and their retention times. The retention times can be compared with the results for known compounds to help identify the compounds in the mixture.

Question 20

What does the mass spectrometer do

Answer 20

The mass spectrometer gives further data that a computer can use quickly to identify the individual compounds

Question 21

What is the link between the mass spectrometer and the relative molecular mass

Answer 21

The mass spectrometer can be used to find the relative molecular made of a compound from its molecular ion peak