Chem: Acids, Alkalis + Chemical tests

What range of values does the pH scale cover, and what value represents a neutral solution?

The pH scale runs from 0 to 14, where pH 7 represents a neutral solution (e.g., pure water).

What are the characteristic colors of litmus, phenolphthalein, and methyl orange in acidic versus alkaline solutions?

Litmus is red in acidic and blue in alkaline; phenolphthalein is colourless in acidic and bright pink in alkaline; methyl orange is red in acidic and yellow in alkaline solutions.

What ions define an acid and an alkali in aqueous solutions?

Acids produce hydrogen ions ($H^+$); alkalis produce hydroxide ions ($OH^-$).

How is neutralisation defined in terms of proton transfer and ionic equations?

Neutralisation is a proton transfer reaction where an acid donates protons ($H^+$) that are accepted by a base; the ionic equation is $H^+_{(aq)} + OH^-_{(aq)} \rightarrow H_2O_{(l)}$.

What types of salts are produced when hydrochloric, sulfuric, and nitric acids react with bases?

Hydrochloric acid produces chloride salts; sulfuric acid produces sulfate salts; nitric acid produces nitrate salts.

What general products are formed in the reaction between an acid and a metal oxide or metal hydroxide?

A salt and water ($Acid + Metal\ Oxide/Hydroxide \rightarrow Salt + Water$).

What product is formed when an acid reacts with ammonia gas or aqueous ammonia?

An ammonium salt ($Acid + Ammonia \rightarrow Ammonium\ Salt$).

What general products are formed when an acid reacts with a metal carbonate?

A salt, water, and carbon dioxide ($Acid + Metal\ Carbonate \rightarrow Salt + Water + Carbon\ Dioxide$).

What is the primary purpose of carrying out a titration experiment?

Titrations allow you to find out exactly how much acid is needed to neutralise a specific quantity of alkali, or vice versa.

What specific apparatus is used to measure out the initial fixed volume of alkali into the conical flask?

A pipette and pipette filler are used to accurately measure out a set volume (e.g., $25\text{ cm}^3$) of alkali.

Why should you fill a burette below eye level during a titration practical?

To avoid the risk of spilling acid into your eyes if the solution overflows.

Why is universal indicator not suitable for use in titration experiments?

Universal indicator changes colour gradually across a wide pH scale, making it difficult to judge the exact end-point accurately.

What are the rules of solubility for common sodium, potassium, ammonium, nitrate, chloride, sulfate, carbonate, and hydroxide salts?

Sodium, potassium, ammonium, and nitrate salts are all soluble; chlorides are soluble except silver and lead chloride; sulfates are soluble except lead, barium, and calcium sulfate; carbonates and hydroxides are insoluble except those of sodium, potassium, and ammonium (plus calcium hydroxide being slightly soluble).

How do you prepare a pure, dry sample of an insoluble salt via a precipitation reaction?

Mix two soluble salt solutions together to form the precipitate, filter the mixture through filter paper in a funnel, wash the residue with deionised water to remove soluble compounds, then scrape the precipitate onto fresh filter paper and dry in an oven or desiccator.

Which two soluble compounds can be mixed to produce insoluble lead sulfate ($PbSO_4$)?

Lead nitrate ($Pb(NO_3)_2$) and magnesium sulfate ($MgSO_4$).

Why is deionised water used to rinse the equipment and precipitate during the preparation of lead sulfate?

To ensure all soluble impurities and stray ions (like magnesium nitrate) are thoroughly washed away without introducing new mineral contaminants.

How do you calculate the unknown concentration of an acid from titration data given alkali volume and concentration?

1) Convert alkali volume to $\text{dm}^3$ and calculate alkali moles ($\text{moles} = c \times v$); 2) Use the balanced symbol equation mole ratio to determine acid moles; 3) Divide acid moles by acid volume in $\text{dm}^3$ to find acid concentration.

How do you test for carbonate ions ($\text{CO}_3^{2-}$), and what is observed?

Add dilute hydrochloric acid ($\text{HCl}$) to the sample; if carbonates are present, carbon dioxide gas ($\text{CO}_2$) is released, causing effervescence.

What is the ionic equation for the reaction of carbonate ions with acid?

\text{CO}_3^{2-}_{(aq)} + 2\text{H}^+_{(aq)} \rightarrow \text{CO}_{2(g)} + \text{H}_2\text{O}_{(l)}.

How do you test for sulfate ions ($\text{SO}_4^{2-}$)?

Add dilute hydrochloric acid ($\text{HCl}$), followed by barium chloride solution ($\text{BaCl}_2$).

What observation indicates the presence of sulfate ions?

A white precipitate of barium sulfate ($\text{BaSO}_4$) is formed.

Why is hydrochloric acid added before adding barium chloride in the sulfate test?

To react with and eliminate any traces of carbonate or sulfite ions that would also form a white precipitate and distort the results.

How do you test for halide ions ($\text{Cl}^-$, $\text{Br}^-$, $\text{I}^-$)?

Add dilute nitric acid ($\text{HNO}_3$), followed by silver nitrate solution ($\text{AgNO}_3$).

What precipitate colors are produced by chloride, bromide, and iodide ions in the silver nitrate test?

Chloride ions form a white precipitate of silver chloride ($\text{AgCl}$); bromide ions form a cream precipitate of silver bromide ($\text{AgBr}$); iodide ions form a yellow precipitate of silver iodide ($\text{AgI}$).

Why is nitric acid used instead of hydrochloric acid when testing for halides?

To clear out any interfering carbonate or sulfite ions without adding chloride ions from $\text{HCl}$, which would give a false positive white precipitate.

What are the chemical tests and positive results for chlorine, oxygen, carbon dioxide, hydrogen, and ammonia gas?

Chlorine bleaches damp blue litmus paper white; oxygen relights a glowing splint; carbon dioxide turns limewater cloudy; hydrogen makes a "squeaky pop" with a lighted splint; ammonia turns damp red litmus paper blue.

How can anhydrous copper(II) sulfate be used to test for the presence of water?

Adding water to white anhydrous copper(II) sulfate powder converts it into blue hydrated copper(II) sulfate crystals.

How do you test if a water sample is chemically pure?

Check its physical fixed points: pure water boils at exactly 100 °C and freezes at 0 °C.

Describe the step-by-step method for preparing a pure

dry sample of a soluble salt using an acid and an insoluble base. 1) Heat the acid gently in a water bath inside a fume cupboard; 2) Add the insoluble base in excess until no more dissolves and solid sinks to the bottom; 3) Filter off the excess solid to leave the salt solution; 4) Heat the solution gently in an evaporating dish to evaporate some water; 5) Leave to cool and crystallise

Why is the insoluble base added in excess when making a soluble salt? To ensure all the acid is completely reacted and neutralised

preventing leftover acid in the final product.

Why can you not use the excess base method when making a soluble salt from an acid and an alkali? Both reactants are soluble

so adding excess alkali would contaminate the salt solution with no easy way to filter it out.

How do you prepare a pure

dry sample of a soluble salt using an acid and an alkali? 1) Perform a titration using an indicator to find the exact volumes of acid and alkali needed for neutralisation; 2) Repeat the reaction using the exact same volumes without the indicator; 3) Evaporate some water and leave the solution to crystallise

How do you clean and prepare a wire loop before performing a flame test? Clean a platinum wire loop by dipping it in dilute hydrochloric acid ($\text{HCl}$) and holding it in the hottest blue flame of a Bunsen burner until it burns without colour.

What flame colours are produced by Lithium ($\text{Li}^+$)

Sodium ($\text{Na}^+$)

What test is used to identify metal cations that form coloured insoluble hydroxide precipitates? Add a few drops of sodium hydroxide solution ($\text{NaOH}$) to the mystery solution.

What are the precipitate colours and ionic equations for Copper(II) ($\text{Cu}^{2+}$)

Iron(II) ($\text{Fe}^{2+}$)

How do you test a sample for ammonium ions ($\text{NH}_4^+$)? Add sodium hydroxide solution ($\text{NaOH}$) to the sample and heat gently; if ammonium ions are present

smelly ammonia gas ($\text{NH}_3$) is produced