Amount of substance (DONE)

In the heating a crucible experiment why shouldn't small amounts of the solid be used

small amounts of the solid, e.g. 0.100g, should not be used in this experiment as errors in weighing are too high. 

In the heating a crucible experiment why is the lid important 

The lid improves accuracy of the experiment as it prevents loss of solid from the cruicble but should be loose fitting to allow gas to escape. 

In the heating a crucible experiment why does the cruicible need to be dry

because otherwise a wet cruicble would give an inaccurate test result. 
- It would cause mass loss to be too large as water would be lost when heating.

for the heating a crucible experiment what should not be used and why

Large amount of hydrated calcium sulphate, such as 50g, should not be used in the experiment as the decomposition is likely to be incomplete. 

What can the method for heating a crucible also be used for 

This method could be used for measuring mass lost in various thermal decomposition reactions and also for mass gain when reacting magnesium in oxygen

.

1. Weigh an empty clean dry crucible and lid.

2. Add 2g of hydrated calcium sulfate to the crucible and weigh again

3. Heat strongly with a Bunsen for a couple of minutes

4. Allow to cool

5. Weigh the crucible and contents again

6. Heat crucible again and reweigh until you reach a constant

7. mass ( do this to ensure reaction is complete).

.

Anhydrous Copper (II) nitrate (V)

.

Hydrated copper (II) nitrate (V)

A hydrated salt contains […]

A hydrated salt contains water of crystallisation

fill in the blank

answer

analysis

Investigating the chemical composition of a substance 

Finding formulae by experiment 

You can predict the formula of an ionic compound from its ions, but if you do not know which ions are in a compound, the formula can be worked out from the results of experiments. 

How do you find the molecular formula 

• Find the empirical formula 

• From the relatively molecules mass (Mr) work out how many times the mass of the empirical formula fits into the Mr.

• The Mr does not need to be exact to turn an empirical formula into the molecular formula because the molecular formula will be a whole number multiple of the empirical formula.

Molecular formula

A molecular formula is the actual number of atoms of each element in the compound.

What can finding the empirical formula method be used for

• The masses of each element in a compound

• Percentage masses of each element in a compound

What is the general method of finding the empirical formula

• Divide each mass (or % mass) by the atomic mass of the element

• For each of the answers from step one divide by the smallest one of those numbers

• Sometimes the Number calculated in step two will need to be multiplied up to give a whole Numbers.

• These whole numbers will be the empirical formula

An empirical formula

the simplest ratio of atoms of each element in the compound

.

164.1

NaCl relative formula mass

58.5

True or false Relative formula mass is for simple molecules

False - For giant structures

Relative formula mass

compares the mass of a formula unit with the mass of an atom of carbon-12.

Mr of H2O

18.0

True or false Relative molecular mass is for simple molecules

True 

  Relative molecular mass, Mr  

Compares the mass of a molecule with the mass of an atom of carbon-12

  Relative atomic mass 

average mass of one atom compared to one twelfth of the mass of one atom of carbon 12 

If you are given a mixture of different sig fig what do you do

use the smallest 

kg to tonne

divide by 1000

g to kg

divide by 1000

mg to g 

divide by 1000

Amount of substance n, mass m, and molar mass M are linked by what equation

.

Molar mass of C

.

How do you find the molar mass of an element? 

.

.

14.0+(16.0x2) = 46.0  g mol-1

Molar mass of   CaCO_3

40.1+12.0+(16.0x3) = 100.1 

How can molar mass be calculated for a compound? 

By adding up the mass number of each element in the compound

Molar mass 

The mass in grams of 1 mole of a substance and is given the unit of   g mol-1

True or false Avogadro's constant cannot be used for atoms, molecules and ions, only atoms

False - they it can be used for atoms, molecules and ions 

How much atoms will there be in one mole of sodium ions?

    6.02×10²³

How much atoms will there be in one mole of carbon molecules?

  6.02×10²³

What will the mass of one mole of iron atoms be?

55.8g

What will the mass of one mole of magnesium atoms be?

24.3g

What will the mass of one mole of hydrogen atoms be?

1.0g

What will the mass of one mole of carbon atoms be?

12.0g

Avogadro constant Na

.

One mole is the amount of substance that contains […] particles. which is know as […].

One mole is the amount of substance that contains 6.02x10^{23} particles. which is know as Avogadro constant.

The mole 

The mole is the amount of substance in grams that has the same number of particles as there are in atoms in 12 grams of carbon-12

what is a solution?

A solution is a mixture formed when a solute dissolves in a solvent.

what is the most common solvent used to form aqueous solutions, what state of matter can the solute be in while using this solvent.

In chemistry we most commonly use water as the solvent to form aqueous solutions. The solute can be a solid, liquid or a gas.

How do we calculate Molar concentration

This is calculated by dividing the amount in moles of the solute by the volume of the solution.

The volume is measure is dm3.

The unit of molar concentration is mol dm-3 or M.

1m³ in cm³

100cmx100cmx100cm = 1000000 cm³

dm3/1 litre in cm3

10cmx10cmx10cm = 100cm3

cm3 to 1mL

1cmx1cmx1cm = 1 mL

1 m3 to dm3

x1000 → 1000 dm3

Fill in the blanks

answers

The concentration of a solution can also be measured in terms of […] of solute per volume of solution

The concentration of a solution can also be measured in terms of mass of solute per volume of solution

Equation for mass concentration

Mass concentration = mass/volume

Unit of mass concentration: g dm-3

Unit of Mass: g

Unit of Volume: dm3

How do we turn concentration measured in mol dm-3 into concentration measured in g dm-3

To turn concentration measured in mol dm-3 into

concentration measured in g dm-3:

• multiply by Mr of the substance

• conc in g dm-3 = conc in mol dm-3 x Mr

• The concentration in g dm-3 is the same as the mass of solute dissolved in 1dm3

What happens when soluble ionic solids dissolve in water and what can this lead to

• When soluble ionic solids dissolve in water they will dissociate into separate ions.

• This can lead to the concentration of ions differing from the concentration of the solute.

Method of making a solution

• Weigh the sample bottle containing the required mass of solid on a 2 dp balance.

• Transfer to beaker and reweigh sample bottle

• Record the difference in mass

• Add 100cm3 of distilled water to the beaker. Use a glass rod to stir to help dissolve the solid.

• Sometimes the substance may not dissolve well in cold water so the beaker and its contents could be heated gently until all the solid had dissolved.

• Pour solution into a 250cm3 graduated flask via a funnel.

• Rinse beaker and funnel and add washings from the beaker and glass rod to the volumetric flask.

• make up to the mark with distilled water using a dropping

• pipette for last few drops.

• Invert flask several times to ensure uniform solution.

what can we do alternatively in the making solution experiment

Alternatively the known mass of solid in the weighing bottle could be transferred to beaker, washed and washings added to the beaker.

What must we remember to prevent any errors in the making solutions experiment

We must remember to fill so the bottom of the meniscus sits on the line on the neck of the flask.

With dark liquids like potassium manganate it can be difficult to see the meniscus.

Method on Diluting a solution

• Pipette 25cm3 of original solution into a 250 cm3 volumetric flask

• make up to the mark with distilled water using a dropping pipette for last few drops.

• Invert flask several times to ensure uniform solution.

In a diluting a solution experiment, Using a volumetric pipette is more […] than a measuring cylinder because it has a smaller […]

Use a teat […] to make up to the mark in volumetric flask to ensure volume of solution is accurately measured and one doesn't go over the […]

In a diluting a solution experiment, Using a volumetric pipette is more accurate than a measuring cylinder because it has a smaller uncertainty

Use a teat pipette to make up to the mark in volumetric flask to ensure volume of solution is accurately measured and one doesn't go over the line

Calculating Dilutions

• Diluting a solution will not change the amount of moles of solute present but increase the volume of solution and hence the concentration will lower

1. amount= volume x concentration

• If amount of moles does not change then:

2. new diluted concentration = original concentration x (Original volume/new diluted volume)

• The new diluted volume will be equal to the original volume of solution added + the volume of water added.

What are the safety hazards for the dilutions experiment

Irritant - dilute acid and alkalis- wear googles

Corrosive- stronger acids and alkalis wear goggles

Flammable - keep away from naked flames

Toxic - wear gloves- avoid skin contact- wash hands after use

Oxidising- Keep away from flammable / easily oxidised materials

The ideal gas equation applies to all gases and mixtures of gases. If a mixture of gases is used the value […] will be the total moles of all gases in the mixture.

The ideal gas equation applies to all gases and mixtures of gases. If a mixture of gases is used the value n will be the total moles of all gases in the mixture.

What is the Ideal Gas Equation?

PV = nRT

Unit of Pressure (P):Pa

Unit of Volume (V): m3

Unit of Temp (T): K

n= moles

R = 8.31 JK-1mol-1

How do we convert degrees Celsius into Kevin

add 273

Use of gas syringe

Gas syringes can be used for a variety of experiments where the volume of a gas is measured, possibly to

work out moles of gas or to follow reaction rates.

What does the volume of a gas depend on

The volume of a gas depends on pressure and temperature so when recording volume it is important to note down the temperature and pressure of the room.

How can moles of gas be calculated from gas volume

Moles of gas can be calculated from gas volume (and temperature and pressure) using ideal gas equation PV = nRT or using the molar gas volume (1mol gas =24dm3 at room temperature and pressure.

What are some potential errors in using a gas syringe

• gas escapes before bung inserted

• syringe sticks

• some gases like carbon dioxide or sulphur dioxide are soluble in water so the true amount of gas is not measured.

Draw a gas syringe

.

1 mole of any gas at room pressure (1atm) and room temperature 25 degrees Celsius will have the volume of […]

24 dm³

Equal volumes of any gases measured under the same

conditions of temperature and pressure contain what?

equal numbers of molecules (or atoms if the gas in monatomic)

How can Volumes of gases reacting in a balanced equation be calculated?

Volumes of gases reacting in a balanced equation

can be calculated by simple ratio

The mole is the amount of substance in grams that has the same number of particles as there are atoms in […].

The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

What is the equation that links No of particles, amount of substance and Avogadro’s constant

No of particles = amount of substance (in mol) x Avogadro’s constant

Equation for density

.

Converting quantities between different substances ysubg a balanced equation steps

Typically we are given a quantity of one substance and are asked to work out a quantity for another substance in the reaction.

What is the equation for percentage yield

.

How can percentage yield be lowered

% yield in a process can be lowered through incomplete reactions, side reactions, losses during transfers of substances, losses during purification stages.

Steps on finding the limiting and excess reactant

1. calculate amount, in mol for both reactants

2. Use balanced equation to work out which reactant is in excess

3. Use balanced equation to work out amount in mol of the substance formed

4. Calculate the mass of the substance

Equation for percentage atom economy

.

true or false we can/should use balancing numbers when calculating percentage atom economy

True

Why is atom economy so important

• Sustainable chemistry requires chemists to design processes with high atom economy that minimise production of waste products.

• Reactions where there is only one product where all atoms are used making product are ideal and have 100% atom economy. e.g. CH2=CH2 + H2 -> CH3CH3

• If a process does have a side, waste product the economics of the process can be improved by selling the bi-product for other uses