A sodium salt X in water turns litmus red and produces a gas that turns lime water milky when reacted with sodium carbonate. With BaCl2, X forms a white precipitate insoluble in dilute HCl. X is
NaHSO4 is acidic (turns litmus red), reacts with Na2CO3 to produce CO2 (milky lime water), and forms BaSO4 with BaCl2, insoluble in dilute HCl.
The alkanol obtained as a by-product during soap production is
Saponification of fats/oils with a base produces soap and glycerol (propane-1,2,3-triol).
The flame used by welders for cutting metals is
Oxy-acetylene flame (~3500°C) is ideal for cutting metals due to its high temperature.
Consecutive members of an alkane homologous series differ by
Alkanes (CnH2n+2) differ by a CH2 unit (e.g., CH4 to C2H6).
An element with electronic configuration 1s²2s²2p⁶3s²3p² belongs to
The configuration ends in 3p² (e.g., silicon), placing it in the p-block (Group 14).
CuSO4·5H2O was heated at 120°C. Wt of crucible = 10.00 g; Wt of crucible + CuSO4·5H2O = 14.98 g; Wt of crucible + residue = 13.54 g. How many water molecules were lost? [Cu=63.5, S=32, O=16, H=1]
Mass of CuSO4·5H2O = 4.98 g. Residue = 3.54 g. Water lost = 1.44 g. Moles of water = 1.44 / 18 = 0.08 mol. Moles of CuSO4 = 3.54 / 159.5 ≈ 0.0222 mol. At 120°C, CuSO4·5H2O loses 2 waters, forming CuSO4·3H2O.
The three-dimensional shape of methane (CH4) is
Methane’s carbon is sp³ hybridized, forming four C-H bonds in a tetrahedral arrangement (109.5°).
The product of ethanol and ethanoic acid with concentrated H2SO4 is
Ethanol and ethanoic acid form ethyl ethanoate (ester) via esterification.
The IUPAC name for CH3CH2CH2OH is
CH3CH2CH2OH has 3 carbons with -OH on the first carbon, named propan-1-ol.
The process converting starch to ethanol is
Fermentation converts starch (via glucose) to ethanol using yeast.
A mixture of NaCl, NH4Cl, and CaCO3 is best separated by
Water dissolves NaCl and NH4Cl, leaving CaCO3 (filtered). NH4Cl sublimes upon heating.
Which relationship represents ideal gas behavior?
Ideal gas law (PV = nRT) implies PV ∝ T at constant n.
Which gas turns damp red litmus paper blue?
NH3, a base, turns red litmus blue. Others are acidic.
The flame color imparted by calcium ions is
Calcium ions produce a brick-red flame.
For the endothermic reaction M + N ⇌ P, ΔH = +Q kJ, what increases [P]?
Endothermic reactions favor products at higher temperatures (Le Chatelier’s principle).
In which reaction is iron oxidized?
In A, Fe(0) → Fe²⁺ (oxidation). Others involve no Fe oxidation or reduction.
What mass of silver is deposited when 2 A is passed through AgNO3 for 4830 s? [Ag=108, F=96500 C/mol]
Charge = 2 × 4830 = 9660 C. Ag⁺ + e⁻ → Ag. Mass = (9660 / 96500) × 108 ≈ 2.16 g.
In Fe + Cu²⁺ → Fe²⁺ + Cu, iron displaces copper because
Iron, higher in the reactivity series, displaces copper.
The IUPAC name for CH3C(CH3)=CH2 is
CH3C(CH3)=CH2 has a 3-carbon chain, double bond at position 1, methyl on carbon 2: 2-methylprop-1-ene.
How many isomers exist for C3H6Br2?
C3H6Br2 has 4 structural isomers: 1,1-, 1,2-, 1,3-, and 2,2-dibromopropane.
Burning sulphur in oxygen produces a gas that forms
S + O2 → SO2, which forms H2SO3 in water.
Na2CO3·10H2O losing water on exposure to air is
Efflorescence is the loss of water of crystallization.
During electrolysis of molten NaCl, what occurs at the anode?
At the anode, 2Cl⁻ → Cl2 + 2e⁻ (oxidation).
Crude oil pollutants in water are best removed by
Detergents emulsify oil for removal.
An electronegative element
Electronegative elements (e.g., halogens) gain electrons.
Solutions with pH 3.0, 5.0, 9.0 are X, Y, Z. Which is true?
pH 3.0 (X) is acidic, 5.0 (Y) is slightly acidic, 9.0 (Z) is basic. Z is least acidic.
For reactions: (1) H2 + ½O2 → H2O, ΔH = -286 kJ; (2) C + O2 → CO2, ΔH = -394 kJ, which is true?
Both are exothermic. Reaction 2 releases more heat (-394 kJ vs. -286 kJ).
Which metals react with dilute HCl?
Mg, Fe, Zn react with HCl, being above hydrogen in the reactivity series.
Stainless steel is an alloy of
Stainless steel contains iron, carbon, and chromium.
What volume of 0.5 M H2SO4 neutralizes 20 cm³ of 0.1 M NaOH? [H2SO4 + 2NaOH → Na2SO4 + 2H2O]
Moles of NaOH = 0.1 × 0.02 = 0.002 mol. H2SO4:NaOH = 1:2, so moles of H2SO4 = 0.001 mol. Volume = 0.001 / 0.5 = 0.002 L = 5 cm³.
Which gas pair does not react with oxygen at 100–400°C?
CO2 and N2 are stable and do not react with O2 at 100–400°C.
The extraction method for aluminum is
Aluminum is extracted via electrolysis (Hall-Héroult process).
To prepare Cu(NO3)2 from CuO, which step is incorrect?
H2SO4 forms CuSO4, not Cu(NO3)2. HNO3 is needed.
To obtain >95% ethanol from palm wine, use
Fractional distillation with a dehydrant (e.g., CaO) ensures >95% ethanol purity.
Increasing gas pressure at constant temperature
Pressure increase compresses gas, increasing density.
2.5 g of hydrated BaCl2 gave 2.13 g anhydrous BaCl2. How many water molecules were lost? [Ba=137, Cl=35.5, H=1, O=16]
Water lost = 2.5 - 2.13 = 0.37 g. Moles of BaCl2 = 2.13 / 208 ≈ 0.01024 mol. Moles of water = 0.37 / 18 ≈ 0.02056 mol. Ratio ≈ 2.
3.06 g of KClO3 saturates 10 cm³ water at 25°C. What is the solubility? [K=39, Cl=35.5, O=16]
Molar mass of KClO3 = 122.5 g/mol. Moles = 3.06 / 122.5 ≈ 0.025 mol. Solubility = 0.025 / 0.01 = 2.5 mol/dm³.
Cracking in the petroleum industry
Cracking breaks large hydrocarbons into smaller fractions like petrol.
Which gas reduces Cl2 and oxidizes H2S?
SO2 reduces Cl2 to HCl and oxidizes H2S to S.
Which solution gives a white precipitate with BaCl2 and a green flame test?
Sulfates form BaSO4 precipitate. CuSO4 gives a green flame.
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