Chemistry B 1

Question 0

How would you measure the concentration of a solution?

Answer 0

The concentration of a solution is measured in moles per dm cubed (or per litre)

So one mole of stuff in a solution has a concentration of 1 mole per litre/dm cubed

1 litre = 1000 cm(cubed) = 1 dm(cubed)

Question 1

What is a moles value and what is its purpose

Answer 1

It is a number with a value of 6.023 * 10(to the power of 23) or 602300000000000000000000

It is used to weigh elements they weigh exactly the same number of grams as the relative atomic mass of an element or compound.

For example if you get exactly one mole worth of carbon-12 atoms it weighs exactly 12g

Question 2

Describe fully the process of titration.

Answer 2

First alkali is put into a flask along with an indicator.

Then the acid is added a little at a time using a burette , making sure the contents are properly mixed.

The indicator changes colour when all the alkali has been neutralised

Question 3

How would you workout the concentration in moles per dm (cubed)?

And how would you work it out in grams per dm (cubed)

Answer 3

For mols per dm (cubed) first you would work out how many moles of the the known substance there is using the formula triangle
Number of moles
Concentration(mole/dm cubed ) x volume (in dm cubed )

If the concentration is in grams you use this triangle
Mass(in grams)
Number of moles x relative formula mass

Question 4

How can you measure the energy released by a chemical reaction in a solution?

Answer 4

By taking the temperature of the reagents , mixing them in a polystyrene cup and the measuring the temperature of the solution at the end of the reaction.

Question 5

Define Endothermic and Exothermic reactions

Answer 5

An Exothermic reactions is one which gives out energy to the surroundings usually in the from of heat and usually shown by a rise in temperature

An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature

Question 6

How is calorimetry calculated?

Answer 6

Energy transferred =

mass of water (g) x specific heat capacity of water x temperature change

Question 7

With energy level diagrams which kind of reaction eventually ends up lower and which one eventually ends up higher. And why?

Answer 7

Exothermic ends up being lower and endothermic ends up being higher.
Exothermic reactions initially start out higher because of activation energy which is the energy needed to break old bonds this is the same for endothermic reactions.

Question 8

What can you add to lower activation energy?

Answer 8

A catalyst

Question 9

How can you get energy from hydrogen and what are its pros and cons?

Answer 9

You can get energy from hydrogen by reacting it with oxygen as the reaction is Exothermic.

Pros
As the reaction just produces water the reaction is very clean
Hydrogen is easy to produce

Cons
You need a special , expensive engine. Although hydrogen can be made from water which there is plenty of, you still need to use energy from another source to make it. It is also explosive

Question 10

When performing a flame test what colour would these metals burn?
Lithium 
Sodium
Potassium
Calcium
Barium

Answer 10

Crimson
Yellow
Lilac
Red
Green

Question 11

When mixed with NaOH what colour do these precipitates form?
Calcium , Ca 2+
Copper(II),Cu 2+
Iron(II), Fe2+
Iron(III), Fe 3+
Aluminium, Al3+
Magnesium, Mg 2+

Answer 11

White
Blue
Green
Brown
White then colourless
White

Question 12

What colour do these tests give
A chloride and a silver chloride
A bromide and a silver bromide
A iodide of silver iodide

Answer 12

White
Cream
Yellow