Chemistry Y11

What is a mole?

A unit used to measure an amount of substance

How many particles are in one mole?

6.02 × 10^23 particles - the Avogadro constant

What types of particles can be counted using moles?

Atoms, molecules, ions or electrons

What is the equation linking mass, relative formula mass and moles?

Mass = Mr x Moles

When using Avogadro's constant, what's the difference between finding molecules/formula units and finding atoms/ions?

Molecules/formula units: moles x Avogadro's constant

Atoms/ions: first calculate the number of molecules/formula units, then multiply by the number of that atom/ion in each particle

2 mol of H₂O contains how many molecules and how many hydrogen atoms?

Molecules: 2 x 6.02 x 10^23 = 1.204 × 10^24
Hydrogen atoms: 1.204 x 10^24 x 2 = 2.408 x 10^24

Balance out the following equation and state each of the masses:
HCl + Mg → MgCl2 + H2

2 HCl + Mg → MgCl2 + H2
HCl = 73g, Mg = 24g, MgCL2 = 95g, H2 = 2g

How can you balance an equation using masses and Mr?

Calculate moles of all substances, write the mole values in a ratio, divide every value in the ratio by the smallest value, the numbers in the ratio determine the big numbers in front of the substance

8.5G of NaNO3 reacts to form 6.9g of NaNO2 and ?g of O2
Calculate the mass of O2 and write a balanced symbol equation using masses and Mr

O2 = 1.6g
2NaNO3 → 2NaNO2 + O2

When using masses and Mr to balanced a symbol equation, what is something key about the ratio?

There must be no decimals, you must multiply to get whole numbers

In a reaction, the reactant that is completely used up is the ____________ → Limits the amount of ________

Limiting reactant, products

How do you determine the limiting reactant of a reaction?

Work out the moles of a substance, which ever is lower is the limiting factor

You have 0.18 mol of CaO and 0.56 mol of H20, what sentence would you write to show the limiting reactant?

If i had 0.18 mol of CaO, I would need 0.18 mol of H20, so I have excess H20 and CaO is the limiting reactant

What is the equation for concentration?

Concentration = Mass / volume

1 dm = ____
1 dm^3 = _____

1 dm = 10cm, 1 dm^3 = 1000cm

For a reaction to occur, what conditions must be met?

Particles must collide, particles must have sufficient energy to overcome activation energy → If both happen, it is a successful collision

What factors affect rate of reaction?

Concentration, temperature, pressure, SA:V, use of a catalyst

How can rate of reaction be measured and what’s units may be used?

Quantity of product used/formed → RoR = Quantity of Reactant used / Time taken OR Quantity of product formed / time taken.
Units = g/s or cm^3/s

Describe the method for surface area to volume ratio practical (change in mass)

Put the acid in the flask on the balance and add the chips.

Plug the flask with cotton wool, start the timer, and record the mass at regular intervals.

The mass falls as gas escapes.

Repeat with smaller chips or powder.

State the hazards for surface area to volume ratio practical (change in mass)

Acid is an irritant, so wear goggles and wipe up spills. The cotton wool stops acid spraying out

State the variables for surface area to volume ratio practical (change in mass)

IV: surface area to volume ratio (chip size)

DV: mass lost over time

CV: mass of chip, volume and concentration of acid, temperature

State the errors for surface area to volume ratio practical (change in mass)

Delay between adding the chips and starting the timer or first reading, so early mass loss is missed. Start the timer straight away, repeat and take a mean

Describe the method for the concentration/disappearing cross practical

Put the flask on the cross.

Mix the solution with water to make different concentrations, keeping the total volume the same.

Add the acid and start the timer.

Look down from above and stop when the cross disappears.

An insoluble solid (the precipitate) forms, so the solution goes cloudy

State the hazards for the concentration/disappearing cross practical

Acid is an irritant, so wear goggles. Solutions can create gas and can trigger asthma, so use small volumes in a ventilated room

State the variables for the concentration/disappearing cross practical

IV: concentration of sodium thiosulfate

DV: time for the cross to disappear

CV: volumes of solution and acid, acid concentration, temperature, same cross, same person judging

Describe the method for the temperature rate of reaction practical (gas)

Warm the acid to a set temperature in the water bath.

Add the metal, quickly put the bung in, and start the timer.

Record the gas volume at regular intervals.

Repeat at higher temperatures

State the hazards for the temperature rate of reaction practical (gas)

Acid is an irritant, so wear goggles. Take care with hot water

State the variables for the temperature rate of reaction practical (gas)

Independent: temperature of the acid

Dependent: volume of gas produced over time

Control: length (or mass) of metal, volume and concentration of acid