>>3.1 - Amount of Substance✔ Flashcards
When doing a titration, what must go in the burette and what must go in the conical flask?
- Solution of known concentration in burette.
- Solution of un-known concentration in conical flask.
What affect will adding water to a solution have?
- Changes its volume and concentration.
- However the number of moles of the original chemical remains the same.
What is the definition of concentration?
- The amount of solute dissolved in 1dm³ of solution.
- moldm⁻³
- Described as the molarity of a solution.
Errors
What affect does leaving the filter funnel in have?
- Leftover acid in funnel may drip into burette.
- Lowers titre volume.
Errors
What affect does having an air bubble under the tap have?
- Incorrect volume measured - air bubble will fill during titration.
- Increases titre volume.
Errors
What affect does not using a conical flask have?
- Acid may spill out when swirling.
Errors
What affect does not swirling have?
- The acid isn’t evenly distributed.
- Increases titre volume.
Errors
What affect does not washing the sides of the conical flask before end point have?
- Acid could be on the sides and not in the main solution, washing the sides with distilled water doesn’t affect moles of either reactant.
- Increases titre volume.
What is the equation for uncertainty in a titration?
- (error value/quantity measured)x100
- If measuring twice, double the uncertainty.
e.g: 25cm³ measuring cylinder with +-0.5
(0.5/25)x100=2%
What three factors add up to give the total error in a titre?
- Reading burette at the start.
- Reading burette at the end.
- Judging the end point to within one drop.
Give one solution to improving % error of a titration:
- Use a more dilute solution in the burette to increase volume added so % is smaller when calculating the uncertainty.
What must chemical reactions be before being used in calculations and why?
- Must be balanced.
- This is because the reacting ratios must be correct.
What is the equation for % yield?
- (actual mass/theoretical mass)x100
What is the equation for atom economy?
- (Mr of desired product/Mr of reactants)x100
- Must include the ratio in the Mr.
In industry why is it desirable to have a high atom economy in a chemical process?
- There is little or no waste product therefore it means the process is more economically viable for industry scale manufacture.
- Having a high atom economy is also beneficial for the environment as it uses less natural resources and therefore often uses less energy.
What is atom economy?
- A measure of the proportion of reactant atoms that become part of the desired product in the balanced chemical equation.
What is 1dm³ in cm³?
- 1000cm³
What is 1m³ in dm³?
- 1000dm³
How do you convert from moldm⁻³ to gdm⁻³?
- Multiply moldm⁻³ by the Mr.
What is the definition of Ar?
- Relative atomic mass is defined as the average mass of an atom of an element relative to 1/12th the Ar of an atom of carbon-12.
What is the definition of Mr?
- Relative molecular mass is defined as the average mass of a molecule of a compound relative to 1/12th the Ar of an atom of carbon-12.
What term is used for the mass of ionic compounds?
- Relative formula mass.
What is the equation for diluting a solution?
- C₁xV₁=C₂xV₂
What is avogadro’s constant?
- 6.022x10²³ particles in 1 mole.
- Allows the number of particles present in a sample of a substance with known mass to be found.
What is the number of elementary entities equal to?
- Number of moles x Avogadro’s constant
What are the three equations for moles?
- Mass/Mr
- Concentration x Volume
- Volume/24dm³ pV=nRT
What is the definition of a mole?
- The number of atoms in 12g of carbon-12.
What can the mole be applied to?
- Electrons, atoms, molecules, ions, formulas and equations.
What is the ideal gas equation?
- pV=nRT
- p=pressure (Pa)
- V=volume (m³)
- n=moles (mol)
- R=gas constant (8.314JK⁻¹mol⁻¹)
- T=temperature (K)
What is the normal atmosphere pressure roughly equal to?
- 101kPa (1atms.)
How do you convert from °C to kelvin?
- Add 273.
- To convert back to °C minus 273.
What is the empirical formula?
- Simplest whole number ratio of atoms of each element in a compound.
What is the molecular formula?
- The true ratio of atoms of each element in a compound.
Empirical Formula/Molecular Formula:
Example: 2.84g of phosphorus oxide contains 1.24g of phosphorus, what is the empirical formula of this compound:
- P₂O₅
- You work out the moles of each element then you divide the moles of each element by the smallest moles present to get a ratio.
- In this case the ratio isn’t a whole number so we have to multiply both by two to get the empirical formula.
- P
Mass: 1.24g
Mr: 31
Moles: 0.04
Ratio: 1 - O
Mass: 1.60g
Mr: 16
Moles: 0.1
Ratio: 2.5
What are hydrated compounds?
- These are compounds that have water bonded to them, this affects the Mr of the compound.
e.g: CuSO₄.5H₂O (5 waters bonded to the salt.)
How can you find the mass of the solid in a hydrated compound?
- The water can be removed by heating until no mass change is observed, and then we can measure the mass of water that is lost and the mass of the solid remaining.
deal Gas Equation:
Example: 30cm³ of methane reacts with 10cm³ of oxygen forming CO₂ and water. What will the total volume of the reaction be when the reaction is complete?
(assume 298K, 100kPa throughout)
⓵ CH₄ + 2O₂ → CO₂ + 2H₂O (we don’t know if the moles are balanced)
⓶ Find the moles of each reactant using the equation:
CH₄
100000x(30x10⁻⁶)/8.314x298=1.21x10⁻³
O₂
100000x(10x10⁻⁶)/8.314x298=4.03x10⁻⁴
↓
Limiting Factor as from the equation we know that 4x10⁻⁴ moles of O₂ can react with only 2x10⁻⁴ moles of methane, therefore we have excess methane (1.21x10⁻³) so oxygen will run out first.
⓷ Refer to table
⓸ Total up all the final moles and put into the equation:
V=(1.6x10⁻³)(8.314)(298)/100000= 3.96x10⁻⁵m
What is the equation for Avogadro’s constant, L?
- Mr/Mass
