chemistry exam Flashcards
Distinguish between an element and a compound:
Element: cannot be broken down chemically into simpler substances / composed only of atoms with the same atomic number / substance listed on the periodic table. Compound: composed of two or more elements chemically combined.
Distinguish between an atom and a molecule:
Atom: smallest particle of an element. Molecule: smallest particle of an element or of a compound that can exist independently / two or more atoms joined chemically.
Distinguish between ionic and covalent bonding:
Ionic: involves transfer of electrons / involves attraction between oppositely charged ions / arises where difference in electronegativity values (between the bonding atoms) > 1.7. Covalent: involves sharing of electrons / involves mutual attraction for shared electrons / arises where difference in electronegativity values (between the bonding atoms) ≤ 1.7.
Define an atomic orbital:
Region or space (around the nucleus of an atom) where the probability of finding an electron is high / where an electron is likely to be found.
Write the s, p electron configuration for a lithium atom:
1s² 2s¹ / [He] 2s¹.
Write the s, p electron configuration for a chlorine atom:
1s² 2s² 2p⁶ 3s² 3p⁵ / [Ne] 3s² 3p⁵.
Describe how you would carry out a flame test on a sample of LiCl:
(Allow ‘inoculating loop’ or ‘spatula’ for ‘platinum wire’; clear labelled diagram acceptable for some or all points).
What colour does LiCl give to a flame?
Red / crimson.
Define the electronegativity of an element:
Measure of attraction / force or power of attraction / relative attraction (an atom in a molecule has) for a shared pair of electrons / for electrons in a covalent bond.
Plot the electronegativity values versus atomic numbers for elements Li to F and F to I:
(Y-axis labelled electronegativity and X-axis labelled atomic number; points plotted appropriately).
Explain the decrease in electronegativity values shown down Group 17:
Additional shell added / increasing atomic radius / more screening or shielding (of nucleus).
Use electronegativity values to predict the type of bonding in the compound NF3:
“3.98 – 3.04 / 0.94 → polar / polar covalent.”Question
Explain the underlined term:
A solution of known concentration.
Name the piece of apparatus shown in Figure 13:
Volumetric flask.
Describe how the dilution could have been carried out:
(25 cm³) pipette used (to add vinegar to volumetric flask) / pipette (first) rinsed with deionised or distilled water and (then) vinegar or solution to be measured out / pipette filler used to fill (pipette) to mark (with vinegar) / (volumetric) flask rinsed with deionised or distilled water / deionised or distilled water added (to flask) until near mark / pipette or dropper used to add last few drops of water / until bottom of meniscus is on mark / (flask) stoppered and inverted several times.
Describe the correct procedure for rinsing a burette for use in this titration:
Rinse with deionised or distilled water / rinse with acid or (diluted) vinegar / rinse with solution it is to deliver or hold.
Describe the correct procedure for filling the burette with the diluted vinegar:
Use funnel / fill above (zero) mark / open tap to fill part below tap / (remove funnel and) adjust (approximately) to zero / use dropper to bring to mark / bottom of meniscus on (zero) mark / no bubbles / clamped vertically.
Name a suitable indicator for use in this titration:
Phenolphthalein.
What colour change would be observed at the end point of the titration?
Pink to colourless.
Explain why it is advisable to use no more than 1 to 2 drops of indicator in a titration:
Indicators are weak acids or weak bases / would interfere with or affect result or accuracy or pH of reaction mixture.
Calculate the molarity of the potassium hydroxide solution that contained 3.36 g of KOH per litre:
Mr = 56; 3.36 / 56 = 0.06 (moles per litre) / 0.06 (M).
Calculate the concentration of CH3COOH in the diluted vinegar in moles per litre:
Using n1 = (V1 × M1) / (V2 × M2) / 18.65 × M1 = 25.0 × 0.06 / (M2) = 0.080 (M).
Calculate the concentration of CH3COOH in the original vinegar in moles per litre:
0.080 × 10 = 0.80 (M).
Calculate the concentration of CH3COOH in the original vinegar in grams per litre:
“Mr = 60; 60 × 0.80 = 48 (g per litre).”Question
