Chemistry Topic 5 Flashcards
What is the definition of a mole?
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 relative atomic mass?
Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.
What is molar mass?
Molar mass is the mass in grams of 1 mole of a substance and is given the unit of g mol⁻¹.
What is the equation for calculating amount for pure solids, liquids, and gases?
amount = mass / Molar Mass
Unit of Mass: grams, Unit of amount: mol
What is the conversion between milligrams and grams?
1000 mg = 1 g
What is the conversion between grams and kilograms?
1000 g = 1 kg
What is the conversion between kilograms and tonnes?
1000 kg = 1 tonne
What is the equation for calculating gas volume?
Gas Volume (dm³) = amount x 24
This equation gives the volume of a gas at room pressure (1 atm) and room temperature (25°C).
How is molar mass for a compound calculated?
Molar mass for a compound can be calculated by adding up the mass numbers (from the periodic table) of each element in the compound.
What is the equation for calculating concentration in solutions?
Concentration = amount / volume
Unit of concentration: mol dm⁻³ or M, Unit of Volume: dm³
What is the equation for calculating amount in solutions?
amount = mass / Mr
What is the conversion from cm² to dm²?
cm² → dm² + 1000
What is the conversion from cm³ to m³?
cm³ → m³ + 1000000
What is the conversion from dm³ to m²?
dm³ → m² + 1000
How should answers be given in terms of significant figures?
Give your answers to the same number of significant figures as the number of significant figures for the data given in a question.
What is a hydrated salt?
A hydrated salt contains water of crystallisation.
What is the formula for hydrated copper (II) nitrate (V)?
Cu(NO3)2 .6H2O
What is the formula for anhydrous copper (II) nitrate (V)?
Cu(NO3)2
What happens when calcium sulfate xH2O is heated?
CaSO4.xH2O(s) → CaSO4(s) + xH2O(g)
What is the first step in the heating method for hydrated salts?
Weigh an empty clean dry crucible and lid.
What should be done after heating the crucible strongly?
Allow to cool and weigh the crucible and contents again.
How much hydrated calcium sulfate should be used in the experiment?
Add 2g of hydrated calcium sulfate to the crucible.
Why should large amounts of hydrated calcium sulfate not be used?
Decomposition is likely to be incomplete.
What effect does a wet crucible have on the experiment?
It would cause mass loss to be too large as water would be lost when heating.
What should be done to ensure the reaction is complete?
Heat the crucible again and reweigh until you reach a constant mass.
How is the mass of H2O calculated in the example?
Calculate the mass of H2O = 3.51 - 1.97 = 1.54g.
What is the molar mass of ZnSO4?
The molar mass of ZnSO4 is 161.5.
What is the ratio of moles of ZnSO4 to H2O in the example?
The ratio is 0.0122.
What is the molar mass of Na2SO4.xH2O?
The molar mass is 322.1.
How is the value of x calculated for Na2SO4.xH2O?
Molar mass xH2O = 322.1 - (23x2 + 32.1 + 16x4) = 180.
What is the calculated value of x for Na2SO4.xH2O?
X = 180/18 = 10.
What is the importance of the lid during the experiment?
The lid improves the accuracy of the experiment as it prevents loss of solid from the crucible.
What should be avoided in terms of sample size for accuracy?
Small amounts of the solid, such as 0.100 g, should not be used as errors in weighing are too high.
What is Avogadro’s Constant?
Avogadro’s Constant is the number of particles in one mole of a substance, which is 6.02 x 10^23.
What is a mole?
A 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.
How do you calculate the number of particles?
Number of particles = amount of substance (in mol) x Avogadro’s constant.
How do you calculate the number of atoms in a sample?
Number of atoms = amount x 6.02 x 10^23
Example: For a 6.00 g sample of tin, amount = 6 / 118.7 = 0.05055 mol.
What is the formula for density?
Density = mass / volume.
How do you calculate mass from density and volume?
Mass = density x volume.
What is the density of ethanol?
The density of ethanol is 0.789 g/cm³.
How do you calculate the number of molecules of ethanol?
Number of molecules = amount x 6.022 x 10^23
Example: For 8.576 mol of ethanol, number of molecules = 8.576 x 6.022 x 10^23.
How do you calculate the amount of chloride ions in a solution?
Amount of chloride ions = amount x 2
Example: For 0.0100 mol of MgCl₂, amount of chloride ions = 0.0100 x 2 = 0.0200 mol.
How do you calculate the number of ions?
Number of ions = amount x 6.02 x 10^23.
How do you calculate the density of gold?
Density = mass / volume
Example: For 980 mol of gold, mass = 980 x 197 = 193060 g, volume = 10,000 cm³, density = 193060 g / 10000 cm³ = 19.3 kg/dm³.
What is an empirical formula?
An empirical formula is the simplest ratio of atoms of each element in the compound.
What is the first step in calculating an empirical formula?
Divide each mass (or % mass) by the atomic mass of the element.
What is the second step in calculating an empirical formula?
For each of the answers from step 1, divide by the smallest one of those numbers.
What is the third step in calculating an empirical formula?
Sometimes the numbers calculated in step 2 will need to be multiplied up to give whole numbers.
What do the whole numbers obtained represent?
These whole numbers will be the empirical formula.
How do you calculate the empirical formula for a compound containing 1.82g of K, 5.93g of I, and 2.24g of O?
Step 1: K=1.82/39.1=0.0465 mol, I=5.93/126.9=0.0467 mol, O=2.24/16=0.14 mol.
Step 2: Divide by the smallest number: K=0.0465/0.0465=1, I=0.0467/0.0465=1, O=0.14/0.0465=3. Empirical formula = KIO.
What is a molecular formula?
A molecular formula is the actual number of atoms of each element in the compound.
How can you deduce the molecular formula from the empirical formula?
From the relative molecular mass (Mr), work out how many times the mass of the empirical formula fits into the Mr.
What types of data can be used to determine an empirical formula?
- Masses of each element in the compound. 2. Percentage mass of each element in the compound.
Does the Mr need to be exact to determine the molecular formula?
No, the Mr does not need to be exact because the molecular formula will be a whole number multiple of the empirical formula.
What is a solution?
A solution is a mixture formed when a solute dissolves in a solvent.
What is the most common solvent used in chemistry?
Water is the most commonly used solvent to form aqueous solutions.
What can a solute be?
A solute can be a solid, liquid, or gas.
How is molar concentration calculated?
Molar concentration is calculated by dividing the amount in moles of the solute by the volume of the solution.
What is the unit of molar concentration?
The unit of molar concentration is mol dm³, also called molar with the symbol M.
What is the formula for concentration?
Concentration = amount / volume
What is the volume measurement in dm?
The volume is measured in dm³.
How many cm³ are in 1 m³?
1 m³ is equivalent to 1,000,000 cm³.
How do you convert m³ into dm³?
To convert m³ into dm³, multiply by 1000.
What is the relationship between dm and m²?
1 dm = 1000 cm².
What is the relationship between cm³ and dm³?
To convert cm³ into dm³, divide by 1000.
How do you calculate the concentration of a solution?
Concentration = amount / volume
What is the formula to find amount from mass?
Amount = mass / Mr
How do you calculate the concentration of a solution made by dissolving 5.00 g of Na₂CO₃ in 250 cm³ of water?
Concentration = 0.0472 / 0.25 = 0.189 mol dm⁻³
How do you calculate the concentration of a solution made by dissolving 10 kg of Na₂CO₃ in 0.50 m³ of water?
Concentration = 94.2 / 500 = 0.19 mol dm⁻³
What is mass concentration?
The concentration of a solution measured in terms of mass of solute per volume of solution.
Mass concentration = mass/volume
What are the units of mass concentration?
Unit of mass concentration: g/dm³
Unit of mass: g, Unit of volume: dm³
What happens when soluble ionic solids dissolve in water?
They dissociate into separate ions, leading to differing concentrations of ions and solute.
Example: NaCl → Na⁺ + Cl⁻
What is the concentration of sodium chloride when 5.86 g is dissolved in 1 dm³ of water?
The concentration of sodium chloride solution would be 0.1 mol/dm³.
The concentration of sodium ions is 0.1 mol/dm³ and chloride ions is also 0.1 mol/dm³.
What is the concentration of magnesium chloride when 9.53 g is dissolved in 1 dm³ of water?
The concentration of magnesium chloride solution would be 0.1 mol/dm³.
The concentration of magnesium ions is 0.1 mol/dm³ and chloride ions is 0.2 mol/dm³.
What is the formula to convert concentration from mol/dm³ to g/dm³?
conc in g/dm³ = conc in mol/dm³ x Mr of the substance.
What is the process to prepare a solution?
Weigh the sample, transfer to a beaker, add distilled water, stir, and make up to the mark in a volumetric flask.
Ensure uniform solution by inverting the flask several times.
What is the chemical equation for the dissociation of sodium chloride?
NaCl(s) → Na⁺(aq) + Cl⁻(aq)
Concentrations: 0.1 mol Na⁺ and 0.1 mol Cl⁻.
What is the chemical equation for the dissociation of magnesium chloride?
MgCl₂(s) → Mg²⁺(aq) + 2Cl⁻(aq)
Concentrations: 0.1 mol Mg²⁺ and 0.2 mol Cl⁻.
How should the meniscus be positioned when filling a volumetric flask?
Fill so the bottom of the meniscus sits on the line on the neck of the flask.
What is the volume of water added to dilute 5.00 cm of 1.00 mol dm-3 hydrochloric acid?
Volume of water added = 100 - 5 = 95 cm³ = 0.1 dm³ = 100 cm³
How is the new volume calculated?
New volume = amount lconc = 0.005 = 1.00 x 0.005
How do you calculate the amount in mol of the original solution?
Amount in mol original solution = conc x vol
What is the new diluted concentration if 50 cm of water are added to 150 cm of a 0.20 mol dm-3 NaOH solution?
New diluted concentration = 0.20 x 0.150
What is the formula for calculating the new diluted volume?
New diluted volume = original volume of solution added + volume of water added
What is the relationship between original and diluted concentrations and volumes?
Original volume x original concentration = new diluted volume x new diluted concentration
What happens to the amount of moles when diluting a solution?
Diluting a solution will not change the amount of moles of solute present but increase the volume of solution.
What should you do to ensure a uniform solution when diluting?
Invert flask several times to ensure uniform solution.
What tool should be used to make up to the mark in a volumetric flask?
Use a teat pipette to make up to the mark.
Why is using a volumetric pipette more accurate than a measuring cylinder?
Using a volumetric pipette is more accurate than a measuring cylinder because it has a smaller uncertainty.
What is the first step in diluting a solution?
Pipette 25 cm³ of original solution into a 250 cm³ volumetric flask.
What is the ideal gas equation?
The ideal gas equation applies to all gases and mixtures of gases.
What does ‘n’ represent in the ideal gas equation for a mixture of gases?
‘n’ represents the total moles of all gases in the mixture.
What is a common problem students face with the ideal gas equation?
Choosing and converting to the correct units.
What is the formula for calculating moles using the ideal gas equation?
moles = PV/RT
How do you calculate the mass of a gas?
Mass = amount x Mr
What is the value of R in the ideal gas equation?
R = 8.31 J K⁻¹ mol⁻¹
How do you convert pressure from kPa to Pa?
100 kPa = 100,000 Pa
How do you convert Celsius to Kelvin?
To convert °C to K, add 273.
What is the volume of gas measured in for the ideal gas equation?
Volume is measured in m³.
What are potential errors in using a gas syringe?
Gas escapes before bung inserted, syringe sticks.
What should be noted when recording the volume of a gas?
The temperature and pressure of the room.
What is the unit of temperature in the ideal gas equation?
The unit of temperature (T) is Kelvin (K).
What is the calculated molar mass (Mr) of a volatile liquid in Example 18?
Mr = 53.4 g mol⁻¹
What is the volume of gas in Example 17?
Volume = 500 cm³ = 0.0005 m³
What is the volume of gas in Example 18?
Volume = 80 cm³ = 0.00008 m³
What is necessary in quality control for testing samples?
It is necessary to do titrations/testing on several samples.
What should be considered when titrating a mixture?
The amount/concentration of the chemical being tested may vary between samples.
What should be recorded during titrations?
Record titre volumes to 2dp (0.05 cm) and both initial and final readings.
How should results be recorded?
Results should be clearly recorded in a table.
What indicates that titration results are accurate?
If 2 or 3 values are within 0.10 cm3, then the results are considered accurate.
What should be done with concordant titre results?
Only make an average of the concordant titre results.
What can lead to errors during titration?
If the jet space in the burette is not filled properly prior to commencing the titration.
What should be used to wash out conical flasks?
Only distilled water should be used.
What happens to the pipette after use?
There will be a small amount of the liquid left in the pipette when emptied.
What is the preferred type of flask for titration?
A conical flask is used in preference to a beaker.
What is the purpose of using a white tile during titration?
To help observe the colour change.
What indicators are used for acid-base titrations?
Methyl orange (yellow to red) and phenolphthalein (pink to colourless).
What safety precautions should be taken during titration?
Wear eye protection and gloves, and treat unknown substances as potentially toxic.
What should be done immediately if a spillage occurs?
Immediately wash affected parts.
What should be done with the burette before adding acid?
Make sure the jet space in the burette is filled with acid.
What should be done with the pipette before use?
Rinse the pipette with alkali.
What are acids and alkalis considered at low concentrations?
Acids and alkalis are irritants and potentially corrosive.
What is the formula to calculate percentage difference?
% = (difference / actual value) x 100
How do you calculate the difference in values?
difference = actual value - calculated value
What is the percentage difference if the calculated Mr is 203 and the real value is 214?
5.41%
What does a discrepancy in results indicate?
It can be explained by the sensitivity of the equipment.
What happens if % uncertainty due to apparatus is greater than the actual value?
There is a percentage difference between the actual value and the calculated value.
What happens if % uncertainty due to apparatus is less than the actual value?
There is no percentage difference between the actual value and the calculated value.
How can you reduce % uncertainty in weighing a solid?
By weighing a larger mass.
What is one method to reduce uncertainty in a burette reading?
Make the titre a larger volume by increasing the volume and concentration of the substance.
What is a way to reduce uncertainties in titration?
Replace measuring cylinders with pipettes or burettes.
How do you calculate maximum percentage apparatus uncertainty?
% uncertainty = (uncertainty / measurement) x 100
What is the uncertainty for a 25 cm pipette?
±0.1 cm
What is the uncertainty for a burette reading?
±0.05 cm
What is the uncertainty of a measurement using a balance?
±0.001 g
What is the uncertainty of a reading based on one judgement?
At least ±0.5 of the smallest scale reading.
What is the uncertainty of a reading based on two judgements?
At least ±1 of the smallest scale reading.
What is a hazard?
A hazard is a substance or procedure that has the potential to do harm.
What are typical hazards in the laboratory?
Typical hazards are toxic, flammable, harmful, irritant, corrosive, oxidizing, and carcinogenic.
How can we minimize the risk of irritants?
For irritants like dilute acids and alkalis, wear goggles.
What precautions should be taken with corrosive substances?
For corrosive substances like stronger acids and alkalis, wear goggles.
What should be done to prevent flammable hazards?
Keep flammable substances away from naked flames.
What is risk in the context of hazardous substances?
Risk is the probability or chance that harm will result from the use of a hazardous substance or procedure.
What precautions should be taken with toxic substances?
Wear gloves, avoid skin contact, and wash hands after use.
What should be done with oxidizing materials?
Keep oxidizing materials away from flammable or easily oxidized materials.
How do hazardous substances in low concentrations compare to pure substances?
Hazardous substances in low concentrations or amounts will not pose the same risks as the pure substance.
What substances can neutralize excess acid safely?
Sodium hydrogen carbonate (NaHCO₃) and calcium carbonate (CaCO₃) are good for neutralizing excess acid because they are not corrosive and will not cause a hazard if used in excess.
What is a suitable substance for dealing with excess stomach acid?
Magnesium hydroxide is suitable for dealing with excess stomach acid as it has low solubility in water and is only weakly alkaline.
What is a key difference between magnesium hydroxide and sodium hydroxide?
Magnesium hydroxide is not corrosive or dangerous to drink, unlike the strong alkali sodium hydroxide.
What are metal displacement reactions?
More reactive metals will displace less reactive metals from their compounds.
Provide an example of a metal displacement reaction.
Mg + CuSO₄ → Cu + MgSO₄
Ionic: Mg + Cu²⁺ → Cu + Mg²⁺
What are halogen displacement reactions?
A halogen that is a strong oxidizing agent will displace a halogen that has a lower oxidizing power from one of its compounds.
Provide an example of a halogen displacement reaction.
Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq)
What are precipitation reactions?
Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed.
Provide an example of a precipitation reaction.
Lead nitrate (aq) + sodium chloride (aq) → lead chloride (s) + sodium nitrate (aq)
What is a precipitate?
A precipitate is a solid formed in a precipitation reaction.
How are insoluble salts typically removed?
The salt would be removed by filtration, washed with distilled water to remove soluble impurities, and then dried on filter paper.
What is the purpose of writing ionic equations for precipitation reactions?
Ionic equations only show the ions that are reacting and leave out spectator ions.
What are spectator ions?
Spectator ions are ions that are not changing state or oxidation number.
Provide an example of writing an ionic equation for a precipitation reaction.
Pb(NO₃)₂(aq) + 2NaCl(aq) → PbCl₂(s) + 2NaNO₃(aq)
Ionic: Pb²⁺(aq) + 2Cl⁻(aq) → PbCl₂(s)
What are metal displacement reactions?
More reactive metals will displace less reactive metals from their compounds.
Provide an example of a metal displacement reaction.
Mg + CuSO₄ → Cu + MgSO₄
Ionic: Mg + Cu²⁺ → Cu + Mg²⁺
What are halogen displacement reactions?
A halogen that is a strong oxidizing agent will displace a halogen that has a lower oxidizing power from one of its compounds.
Provide an example of a halogen displacement reaction.
Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq)
What are precipitation reactions?
Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed.
Provide an example of a precipitation reaction.
Lead nitrate (aq) + sodium chloride (aq) → lead chloride (s) + sodium nitrate (aq)
What is a precipitate?
A precipitate is a solid formed in a precipitation reaction.
How are insoluble salts typically removed?
The salt would be removed by filtration, washed with distilled water to remove soluble impurities, and then dried on filter paper.
What is the purpose of writing ionic equations for precipitation reactions?
Ionic equations only show the ions that are reacting and leave out spectator ions.
What are spectator ions?
Spectator ions are ions that are not changing state or oxidation number.
Provide an example of writing an ionic equation for a precipitation reaction.
Pb(NO₃)₂(aq) + 2NaCl(aq) → PbCl₂(s) + 2NaNO₃(aq)
Ionic: Pb²⁺(aq) + 2Cl⁻(aq) → PbCl₂(s)
