unit 3 chemistry

CaCO3+2CH3COOH---> Ca(CH3COO)2 + CO2 + H2O

collect the gas in either:
- a gas syringe
- an upturned water-filled measuring cylinder in a water trough

-wear eye protection
- ethanoic acid is flammable so keep the room well ventilated and remove any naked flames
-ensure the delivery tube isnt blocked and the volume of gas produced will not damage the tube
- avoid getting ethanoic acid into cuts in the skin
- clear up spillages and broken glassware immediatly

to reduce the amount of gas that is lost before the bung is inserted

- if calcium carbonate is the limiting reagent, increasing the mass of CaCO3 will increase the volume of CO2 produced
- if calcium carbonate is in excess, increasing the mass of CaCO3 willl have no effect on the volume of CO2 produced

- the plunger may not be free moving (may need lubricant)
- some gas may escape before the bung is inserted into the conical flask
- the bung may not be airtight
- some CaCO3 may be lost when transferring it from the weighing boat to the conical flask

ethanoic acid + calcium carbonate ---> Calcium ethanoate + water + carbon dioxide

-Some CO2 amy dissolve in the water so the exact volume isnt measured
- some gas may escape before bung is inserted into the conical flask.
-the bung may not be airtight
- some CaCO3 may be lost when transferring it from the weighing boat to the conical flask

one of the reactants can be placed under an upturned container within the reaction beaker that holds the second reactant. After the bung is securely attached, the reactants can be combined by carefully knocking over the upturned container, releasing the reactant into the reaction mixture

enthalpy change of a reaction is independent of the route taken by the reaction

-wear safety goggles
- avoid skin contact with hydrochloric acid or potassium carbonate as both are irritants
-Clear up spillages and broken glassware immediatly

the reaction takes place at high temprature and requires heating. the enthalpy change can't be measured directly because you have to take into account how much energy was put into the reaction in the first place

a burette is much more accurate and has a higher resolution compared to a measuring cylinder

2KHCO3 (s) ---> K2CO3 (s) + CO2 (g) + H2O (l)

1. weight 3g og KCO3 into a test tube
2. use a burette to add 30cm^3 of 2 mold dm^-3 hydrochloric acid to a polytyrene cup in a beaker
3. measure the intial temprature of the acid
4. add KCO3 to the cup. continually measured the temprature and stir. record the highest temprature reached
5. weigh the empty test tube
6. calculate enthalpy change

-heat loss to the surroundings
-the heat capacity of the solution is generally assumed to be the same as water
- incomplete reaction

Wear eye protection. Phenolphthalein is toxic and flammable so avoid inhaling and keep away from flames. Hydrochloric acid is an irritant so avoid contact with skin. Fill the burette below eye level to avoid splashing acid into your face and eyes. Clear up spillages and broken glassware immediately.

Acid - colourless. Alkali - pink.

A volumetric pipette is more accurate than a measuring cylinder.

The first point at which the indicator changes colour permanently. The point of neutralisation.

Two concordant results (within 0.10 cm³ of each other).

The rough titre is carried out at the start of the titration to gain an approximate idea of how much solution is required from the burette for neutralisation.

The rough titre is not accurate enough.

To the nearest 0.05 cm³.

To the nearest 0.05 cm³. It should match the accuracy of all the values used in the mean calculation.

HCl(aq) + NaOH(aq) -> NaCl(aq) + H₂O(l)

1. Use a pipette to add 25 cm³ of diluted HCl to a conical flask. Add a few drops of phenolphthalein. 2. Pour sodium hydroxide into the burette. Record the initial burette volume. 3. Complete a rough titre. The conical flask should be swirled constantly above a white tile. Stop adding the sodium hydroxide as soon as the end point is reached. 4. Record the final burette volume and calculate the volume of sodium hydroxide solution added. 5. Repeat the titration until two concordant results are obtained. 6. Use the volume of sodium hydroxide to calculate the moles and concentration of hydrochloric acid, using the 1:1 reacting ratio.

To ensure all the reactants are combined so that the reaction is complete.

The larger the titre volume, the smaller the percentage error.

To make the colour change easier to observe.

To make the titre volume larger so that the percentage error is smaller.

Number of moles = concentration (mol dm⁻³) x volume (dm³).

Calculate the number of moles of the alkali using the known volume and concentration (n = C x V). Use the chemical equation to work out the ratio of acid and alkali that react and hence work out how many moles of acid have reacted. Divide the moles of acid by the volume used in neutralisation.

1. Weigh an empty weighing boat. Add approximately 2.5 g of sulfamic acid and reweigh the weighing boat and contents. 2. Dissolve the sulfamic acid in about 100 cm³ of water in a beaker. 3. Transfer the solution into a 250 cm³ volumetric flask. Rinse the beaker with distilled water and add the washings to the flask. 4. Make the solution up to the 250 cm³ mark on the volumetric flask.

Weigh by difference method. The weighing boat is weighed with the solid acid and then again after it is transferred to the beaker in order to calculate if any solid is left in the weighing boat.

Wear eye protection. Sulfamic acid is toxic if ingested so avoid putting it near your face and wash hands after use. Fill the burette below eye level to avoid splashing acid into your face and eyes. Clear up spillages and broken glassware immediately.

a) Acid - red. b) Alkali - yellow. c) Neutral solution - orange.

A volumetric pipette is more accurate than a measuring cylinder.

The first point at which the indicator changes colour permanently.

Two concordant results (within 0.10 cm³ of each other).

It is not accurate enough.

To the nearest 0.05 cm³.

H₃NSO₃(aq) + NaOH(aq) → NaH₂NSO₃(aq) + H₂O(l).

1. Use a pipette to add 25 cm³ of NaOH(aq) to a conical flask. Add a few drops of methyl orange. 2. Pour the sulfamic acid solution into the burette. Record the initial burette volume. 3. Complete a trial titre. The conical flask should be swirled constantly above a white tile. Stop adding the acid as soon as the end point is reached. Record the final burette volume and calculate the volume of sodium hydroxide solution added. 4. Repeat the titration until two concordant results are obtained. Add the acid drop by drop near the end point.

To ensure all the reactants are combined so that the reaction is complete.

The larger the titre volume, the smaller the percentage error.

To make the colour change easier to observe.

To make the titre volume larger so that the percentage error is smaller.

Number of moles = concentration x volume (n = C x V).

Calculate the number of moles of the acid using the known volume and concentration (n = C x V). Use the chemical equation to work out the ratio of acid and alkali that react and hence work out how many moles of alkali have reacted. Divide the moles of alkali by the volume used in neutralisation.

Indicators are very dilute weak acids. They (very slightly) change the volume of the solution in the conical flask and therefore its concentration.

Nucleophilic substitution

Because the carbon-halogen bond is polar (large electronegativity difference between carbon and halogen).

Water

Because there are 2 lone pairs of electrons on each oxygen atom.

The halogen atom present (Cl, Br, or I) and the type of halogenoalkane (primary, secondary, or tertiary).

Wear eye protection; keep halogenoalkanes away from flames (flammable/harmful); avoid contact with corrosive silver nitrate; handle hot water carefully.

1. Mix haloalkanes with ethanol in test tubes. 2. Add AgNO₃ solution and time precipitate formation. 3. Compare rates for different haloalkanes.

To increase temperature, speeding up the reaction rate.

Neutralize excess NaOH with HNO₃ before adding AgNO₃ to avoid masking results with AgOH precipitate.

CH₃CH₂CH₂I + H₂O → CH₃CH₂CH₂OH + I⁻ + H⁺

AgCl - white; AgBr - cream; AgI - yellow.

Halogenoalkanes are insoluble in water; ethanol dissolves them for reaction with water.

Rate increases down Group 7 due to decreasing C-X bond enthalpy (weaker bonds break more easily).

Tertiary hydrolyses fastest (stable carbocation intermediate); primary slowest.

---

(CH₃)₃COH (tertiary alcohol with OH group on central carbon).

Wear gogglesloves; work in a fume cupboard (toxic HCl fumes); keep away from flames (flammable reagents).

(CH₃)₃COH + HCl → (CH₃)₃CCl + H₂O.

To ensure unreacted alcohol remains in the aqueous layer, not the organic product layer.

Separating funnel.

To remove unreacted HCl.

HCl + NaHCO₃ → NaCl + CO₂ + H₂O.

It would hydrolyze the halogenoalkane product, reforming the alcohol.

To remove traces of water (drying agent).

Distillation.

1. Heat impure liquid in a flask with condenser. 2. Collect distillate at boiling point. 3. Use thermometer to monitor temperature.

---

Propanol: -OH (alcohol); propanal: -CHO (aldehyde); propanoic acid: -COOH (carboxylic acid).

Oxidation with acidified K₂Cr₂O₇ and distillation.

Oxidation with acidified K₂Cr₂O₇ under reflux.

Round-bottom flask → Liebig condenser (water in at bottom, out at top) → heat source.

Round-bottom flask → still head with thermometer → condenser → collection flask.

CH₃CH₂CH₂OH + [O] → CH₃CH₂CHO + H₂O.

CH₃CH₂CH₂OH + 2[O] → CH₃CH₂COOH + H₂O.

Orange (Cr₂O₇²⁻) to green (Cr³⁺) colour change.

Reduced to Cr³⁺ (oxidation state +6 → +3).

Wear glovesoggles (corrosive); avoid inhalation/swallowing (harmful).

Propan-1-ol: orange→green with K₂Cr₂O₇; propanal: silver mirror (Tollens’); propanoic acid: fizzes with carbonates.

To prevent violent boiling by promoting smooth vapor formation.

---

Add acid → bubble gas through limewater; white precipitate confirms CO₃²⁻.

Add acidified BaCl₂; white precipitate (BaSO₄) confirms SO₄²⁻.

Add HNO₃ + AgNO₃; observe precipitate colour (AgCl: white; AgBr: cream; AgI: yellow).

Carbonate → sulfate → halide; CO₃²⁻ interferes with other tests.

Bubble through limewater; turns cloudy (white ppt of CaCO₃).

Glowing splint relights.

Clean wire in HCl → dip in sample → observe flame colour.

Li: red; Na: yellow; K: lilac; Ca: orange-red; Sr: red; Ba: pale green.

Decolorizes orange bromine water.

Hydrolyse → test halide ions with AgNO₃/NH₃.

K₂Cr₂O₇/H₂SO₄: orange→green if oxidizable (primary/secondary).

Fehling’s: blue→red ppt; Tollens’: silver mirror.

Effervescence with Na₂CO₃/NaHCO₃ (CO₂ produced).

Molecular ion peak gives Mr; fragment peaks reveal structure.

Peak wavenumbers match bond types (e.g., O-H, C=O).