Quick Review Flashcards - Click to flip and test your knowledge!
Question
In analytical chemistry, what is the primary purpose of qualitative analysis?
Answer
The identification of an unknown substance by chemical tests.
Question
Which two specific alkalis are used in this chapter to identify unknown cations in salt solutions?
Answer
Sodium hydroxide ($NaOH$) and ammonium hydroxide ($NH_4OH$).
Question
Why is sodium hydroxide ($NaOH$) classified as a strong alkali?
Answer
It dissociates completely in solution to furnish $OH^-$ ions.
Question
Why is ammonium hydroxide ($NH_4OH$) classified as a weak alkali?
Answer
It dissociates only partially in solution.
Question
Generally, salts of transition elements (groups 3 to 12) are _____.
Answer
Coloured
Question
Generally, salts of normal elements (groups 1, 2, & 13 to 17) are _____.
Answer
Colourless
Question
State the colour of the $Cu^{2+}$ cation in solution.
Answer
Blue or green
Question
State the colour of the $Fe^{2+}$ cation in solution.
Answer
Green
Question
State the colour of the $Fe^{3+}$ cation in solution.
Answer
Yellow or brown
Question
State the colour of the $Cr^{3+}$ cation in solution.
Answer
Green
Question
State the colour of the $Mn^{2+}$ cation in solution.
Answer
Pink
Question
State the colour of the $Co^{2+}$ cation in solution.
Answer
Blue (pink)
Question
State the colour of the $Ni^{2+}$ cation in solution.
Answer
Green
Question
What is the colour of the permanganate anion ($MnO_4^{1-}$)?
Answer
Pink or purple
Question
What is the colour of the dichromate anion ($Cr_2O_7^{2-}$)?
Answer
Orange
Question
Is the $Zn^{2+}$ cation coloured or colourless?
Answer
Colourless
Question
Is the $Pb^{2+}$ cation coloured or colourless?
Answer
Colourless
Question
Is the $Ca^{2+}$ cation coloured or colourless?
Answer
Colourless
Question
Is the $Mg^{2+}$ cation coloured or colourless?
Answer
Colourless
Question
State the colour of the precipitate formed when $NaOH$ is added dropwise to calcium nitrate solution.
Answer
White
Question
What is the solubility of the $Ca(OH)_2$ precipitate in excess sodium hydroxide?
Answer
Insoluble (or almost insoluble).
Question
State the colour and texture of the precipitate formed when $NaOH$ is added dropwise to magnesium chloride solution.
Answer
Dull white
Question
State the colour of the precipitate formed when $NaOH$ is added to iron (II) sulphate solution.
Answer
Dirty green
Question
State the colour of the precipitate formed when $NaOH$ is added to iron (III) chloride solution.
Answer
Reddish brown
Question
State the colour of the precipitate formed when $NaOH$ is added dropwise to copper (II) sulphate solution.
Answer
Pale blue
Question
What is the appearance of the precipitate formed when $NaOH$ is added dropwise to zinc sulphate solution?
Answer
Gelatinous white
Question
What happens when excess sodium hydroxide is added to a gelatinous white precipitate of zinc hydroxide?
Answer
It dissolves to form a colourless solution.
Question
Name the colourless salt formed when $Zn(OH)_2$ dissolves in excess sodium hydroxide.
Answer
Sodium zincate ($Na_2ZnO_2$).
Question
State the appearance of the precipitate formed when $NaOH$ is added dropwise to lead (II) nitrate solution.
Answer
Chalky white
Question
Name the salt formed when lead (II) hydroxide dissolves in excess sodium hydroxide.
Answer
Sodium plumbite ($Na_2PbO_2$).
Question
Why is no precipitate formed when ammonium hydroxide is added to a solution of calcium nitrate?
Answer
The concentration of $OH^-$ ions is too low to precipitate $Ca(OH)_2$.
Question
What is the solubility of $Fe(OH)_2$ (dirty green ppt) in excess ammonium hydroxide?
Answer
Insoluble
Question
What is the solubility of $Fe(OH)_3$ (reddish brown ppt) in excess ammonium hydroxide?
Answer
Insoluble
Question
What observation is made when excess ammonium hydroxide is added to the pale blue precipitate of copper (II) hydroxide?
Answer
It dissolves to form a deep blue (inky blue) solution.
Question
What is the name of the complex salt formed when $Cu(OH)_2$ dissolves in excess $NH_4OH$?
Answer
Tetrammine copper sulphate (or tetrammine copper hydroxide).
Question
What happens to the white gelatinous precipitate of zinc hydroxide when excess $NH_4OH$ is added?
Answer
It dissolves to form a colourless solution.
Question
Name the complex salt formed when $Zn(OH)_2$ dissolves in excess $NH_4OH$.
Answer
Tetrammine zinc sulphate (or tetrammine zinc hydroxide).
Question
What is the solubility of the chalky white precipitate of lead (II) hydroxide in excess $NH_4OH$?
Answer
Insoluble
Question
Which metals react with hot concentrated caustic alkalis to liberate hydrogen gas?
Answer
Zinc ($Zn$), Lead ($Pb$), and Aluminium ($Al$).
Question
Identify the gas liberated when aluminium reacts with hot concentrated sodium hydroxide.
Answer
Hydrogen ($H_2$)
Question
What is the salt produced when aluminium reacts with hot concentrated potassium hydroxide?
Answer
Potassium aluminate ($KAlO_2$).
Question
Concept: Amphoteric substance
Answer
Definition: A substance (oxide or hydroxide) that reacts with both acids and alkalis to produce salt and water.
Question
Name three metals whose oxides and hydroxides are amphoteric in nature.
Answer
Zinc, aluminium, and lead.
Question
Complete the products for this reaction: $ZnO + 2NaOH \rightarrow$ _____ + $H_2O$
Answer
$Na_2ZnO_2$ (sodium zincate)
Question
Complete the products for this reaction: $Al_2O_3 + 2NaOH \rightarrow$ _____ + $H_2O$
Answer
$2NaAlO_2$ (sodium aluminate)
Question
Complete the products for this reaction: $Pb(OH)_2 + 2NaOH \rightarrow$ _____ + $2H_2O$
Answer
$Na_2PbO_2$ (sodium plumbite)
Question
What are the products of the reaction between aluminium hydroxide and potassium hydroxide?
Answer
Potassium aluminate ($KAlO_2$) and water ($H_2O$).
Question
What is the formula for potassium zincate?
Answer
$K_2ZnO_2$
Question
Which salt solution produces a dirty green precipitate with sodium hydroxide?
Answer
Iron (II) sulphate ($FeSO_4$).
Question
Which salt solution does NOT react with ammonium hydroxide to form a precipitate?
Answer
Calcium nitrate [$Ca(NO_3)_2$].
Question
Identify the cation present in a salt solution that yields a reddish-brown precipitate with $NH_4OH$.
Answer
$Fe^{3+}$ (Iron [III])
Question
Which metal hydroxide is soluble in both excess $NaOH$ and excess $NH_4OH$?
Answer
Zinc hydroxide [$Zn(OH)_2$].
Question
Which metal hydroxide is soluble in excess $NaOH$ but insoluble in excess $NH_4OH$?
Answer
Lead (II) hydroxide [$Pb(OH)_2$].
Question
Which metal hydroxide is insoluble in excess $NaOH$ but soluble in excess $NH_4OH$?
Answer
Copper (II) hydroxide [$Cu(OH)_2$].
Question
What is the balanced equation for the reaction of $FeCl_3$ with $3NaOH$?
Answer
$FeCl_3 + 3NaOH \rightarrow 3NaCl + Fe(OH)_3 \downarrow$
Question
What is the formula of the complex ion formed when zinc hydroxide dissolves in excess $NH_4OH$?
Answer
$[Zn(NH_3)_4]^{2+}$ (as part of tetrammine zinc sulphate/hydroxide).
Question
What is the formula for sodium aluminate?
Answer
$NaAlO_2$
Question
Provide the balanced equation for $Zn$ reacting with $2NaOH$.
Answer
$Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2 \uparrow$
Question
Provide the balanced equation for $PbO$ reacting with $2NaOH$.
Answer
$PbO + 2NaOH \rightarrow Na_2PbO_2 + H_2O$
Question
Which transition element cation listed is pink in solution?
Answer
$Mn^{2+}$