C12

Question 1

What is the definition for a pure substance in chemistry

Answer 1

In chemistry, a pure substance is a single element or compound, not mixed with any other substance

Question 2

What are the characteristics for pure elements and how can these be used

Answer 2

Pure elements and compounds melt and boil at specific temperatures.
Melting point and boiling point data can be used to distinguish pure substances from mixtures

Question 3

What does ‘ pure substance ‘ means in everyday life

Answer 3

In everyday language, a pure substance can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state, eg pure milk

Question 4

What is a formulation and what are some examples

Answer 4

A formulation is a mixture that has been designed as a useful product.
Many products are complex mixtures in which each chemical has a particular purpose. Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.

Question 5

How are formulations made

Answer 5

Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.

Question 6

How can chromatography be used

Answer 6

Chromatography can be used to separate mixtures and can give information to help identify substances.

Question 7

What are the two phases of chromatography

Answer 7

Chromatography involves a stationary phase and a mobile phase.
Separation depends on the distribution of substances between the phases

Question 8

What is an Rf value

Answer 8

The ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent

Question 9

What is the equation to find the Rf value

Answer 9

Rf = distance moved by substance/ distance moved by solvent

Question 10

How do Rf values vary with differen products

Answer 10

Different compounds have different Rf values in different solvents, which can be used to help identify the compounds.
The compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents

Question 11

How can filtration be used

Answer 11

If the product is an insoluble solid that needs to be seperated from a liquid reaction mixture
Can be used to seperate solid impurities in the reaction mixture

Question 12

What are 2 ways to seperate soluble solids from solutions

Answer 12

Evaporation

Crystallisation

Question 13

How is distillation used

Answer 13

To seperate out a liquid from a solution

Can only be used if the liquids have different boiling points

Question 14

How is fractional distillation used

Answer 14

It can seperate out mixtires of liquids with similar boiling points

Question 15

What is flame emision spectroscopy

Answer 15

It can be used to identify metal ions in a solution accurately and find their concentrations

Question 16

How does flame spectroscopy work

Answer 16

A sample is placed under a flame and as the ions heat up their electrons become excited ( move to higher energy levels ) and drop back down again releasing energy as light
This passes through a spectroscope and it’s wavelength is processed, and a line of light is put on a line spectrum

The sample is put into a flame and the light given out is passed through a spectroscope. The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.
The intensity lf the colour reflects the concentration

Question 17

What is a benift of itruemental anysis

Answer 17

Very sensitive (detect tiny amounst)
Very fast
Very acuurate