amount of substance

Question 1

What is a mole?

Answer 1

The way of measuring the amount of substance in chemistry 1 mole of something is 6.023 X1023 molecules of that thing. this is also knows as avogadros number.

Question 2

How can we calculate the number of particles in a substance using avogadros number?

Answer 2

number of particles = avogardos number x number of moles.

Question 3

How can you calculate the muber of moles?

Answer 3

Number of moles = mass [grams] /Mr or Ar.

Question 4

How can you calculate the number of moles in a solution?

Answer 4

number of moles = concentration x volume (dm^3) [cm/1000]

Question 5

How do we work out the theoretical masses using equations?

Answer 5

1. write out the equation and balance it.
2. work out the Mr or Ar of species involved
3. divide the masses using the molecular ratio.
4. times to get the mass made.

Question 6

What is titration?

Answer 6

a device used to work out the concentration of an acid or an alkali

Question 7

How do you do a titration?

Answer 7

• Have the acid or alkali in burette with a known concentration
• have an acid or alkali with an unknown concentration but known volume in the conical flask. add a few drops of indicator
• add the chemical in the burette to the conical flask until the indicator changes colour. this is known as the end point. ad drop by drop near the end point when not doing a rough titre
• read how much chemical was added from the burette to neutralise the chemical in the conical flask. read the bottom of the meniscus.
• record your results to 2 decimal places until you get 2 results that are concordant. (within 0.10 cm of each other)

Question 8

How can you work out the concentration of an acid / alkali using a titration?

Answer 8

• write out the equation and balance it.
• calculate the moles of one of the reactants that isn’t the one your looking for
• use this equation to find out the molar ratio in order to work out the moles of the acid/ alkali you’re looking for.
• calculate the concentration using concentration = moles /vol

Question 9

What is percentage yeild?

Answer 9

the amount of a product produced assuming no products are lost and all reactants react fully.

Question 10

How do you work out the percentage yield?

Answer 10

percentage yield = actual yield / theoretical yield x100 the yield is never 100 %

Question 11

What is atom economy?

Answer 11

How efficient a reaction is?

Question 12

how do you calculate atom economy?

Answer 12

atom economy = molecular mass of desired product/ sum of molecular masses of all reactants x 100

Question 13

Why is atom economy important?

Answer 13

• high atom economies produce less waste and so benefit the environment
• companies will try to use reactions that tend towards 100% atom economy
• high atom economies means that the raw materials used are used more efficiently this is more sustainable.

Question 14

What is the ideal gas equation?

Answer 14

• the number of moles in a specific volume of gas.
• pV = nRt
• where p= pressure in pascals , v= volume in m cubed , n=number of moles
  (mol)R= the gas constant = 8.31jk T = temperature in kelvin.