G8 Mid-term Revision PDF

Extra Revision Exercises For Midterm Exercise 1: Oxygen = 168O = K2L6 since it has 6 valence electrons, it will gain 2 electrons to fill the octet rule so O-2 (anion = negatively charged) Lithium = 73Li = K2L1 since it has 1 valence electron, it will lose 1 electron to fill the octet rule so Li+...

Extra Revision Exercises For Midterm Exercise 1: Oxygen = 168O = K2L6 since it has 6 valence electrons, it will gain 2 electrons to fill the octet rule so O-2 (anion = negatively charged) Lithium = 73Li = K2L1 since it has 1 valence electron, it will lose 1 electron to fill the octet rule so Li+1 (cation = positively charged) Aluminum = 2613Al= K2L8M3 since it has 3 valence electrons, it will lose the 3 electrons to fill the octet rule Al+3 (cation = positively charged) Nitrogen = 147N= K2L5 since it has 5 valence electrons, it will gain 3 electrons to fill the octet rule (anion = negatively charged) Exercise 2 Element Atomic Mass Number of Number of Charge Number Number protons electrons 40 2+ 20Ca 20 40 20 18 +2 (cation) 35 Cl1- 17 35 17 18 -1 (anion) 17 26 Al3+ 13 26 13 10 +3 (cation) 13 16 O 8 16 8 8 0 (neutral) 8 Exercise 3 What is the law of conservation of mass? The law of conservation states that the total quantity/amount of matter is neither created nor destroyed, it only changes its form. Example: A 3g piece of banana is cut into 3 pieces A: 3g (banana) → 1g + 1.5g + 1.7g (Sum = 4.2g) No conservation of mass because mass before (3g) is not equal to the mass after (4.2g) B: 3g (banana) → 1g + 0.7g + 1.3g (Sum= 3g) There is a conservation of mass because mass before (3g) is equal to the mass after (3g) Exercise 4 What is the difference between chemical changes and physical changes? Give examples. In physical change no new substance is formed, the change is reversible, and very little heat or light energy is absorbed or given out during the reaction while in chemical change a new substance is formed, the change is irreversible, and a lot of heat or light energy is involved in the process. Exercise 5 Complete the table: Name of Compound First Element Second Element (you add -ide) Hydrogen Chloride Hydrogen Chlorine Iron nitride Iron Nitrogen Calcium oxide Calcium Oxygen Exercise 6 Graph showing the variation in the speed of sound in different media 8000 7000 Speed of sound (m/s) 6000 5000 4000 3000 2000 1000 0 Medium X Medium Y Medium Z Medium The bar chart above shows the speed of sound in different media X, Y and Z. One is a solid, one is a liquid, and one is a gas. Determine what medium each one is and justify your answer by referring to the graph. Note: Sound travels the fastest in solid then liquid then gas According to the graph, the speed of sound is the highest in medium X at 7000m/s. Then it decreases to 1900m/s in medium Z, and finally decreases to 500m/s in medium Y. This indicates that medium X is a solid because the speed of sound is the highest. Medium Z is a gas because the speed of sound is the lowest. Medium Y is a liquid because the speed of sound was intermediate/moderate. Exercise 7 A student investigates the reaction of iron metal with different types of acid by measuring the time taken release hydrogen gas. The following table shows the data collected from the reaction of a metal with different acids. Type of acid Time taken for hydrogen gas to be released (sec) Strong acid 40 Medium acid 25 Weak acid 10 Interpret the data in the table and to explain how the type and strength of acid affect the reaction time for hydrogen gas release. By referring to the above table, the time taken for hydrogen gas to be released when a metal is mixed with strong acid is 40sec, the time decreases to 25 sec with medium acid and decreases more to 10 sec with a weak acid. This indicates that the fastest reaction happens with a weak acid. Exercise 8 The following table presents several chemical equations. Determine if each is balanced or unbalanced. Then, balance the equations that are not. a. 2Ca + O2 → 2CaO i. S + O2 → SO2 Ca = 1 x 2 = 2 Ca = 1 x 2 = 2 S=1 Ca = 1 O=2 O=1 x2=2 O=2 O=2 Already balanced b. 2Li + F2 → 2LiF j. C + 2H2 → CH4 Li = 1 x 2 = 2 Li= 1 x 2 = 2 C= 1 C=1 O=2 O=1 x2=2 H= 2 x 2 = 2 H=4 c. Mg + Br2 → MgBr2 k. 4Ag + O2 → 2Ag2O Mg = 1 Mg =1 Ag = 1 x 4 = 4 Ag =2 x 2 = 4 Br = 2 Br = 1 O= 2 O=1x2=2 Already balanced d. 4K + O2 → 2K2O l. Ca + 2HCl → CaCl2 + H2 K=1x4=4 K=2 x 2 = 4 Ca = 1 Ca = 1 O= 2 O=1x2=2 H= 1 x 2 = 2 Cl = 2 Cl = 1 x 2 = 2 H=2 e. 2Al + 3Cl2 → 2AlCl3 m. Mg + 2HCl → MgCl2 + H2 Al = 1 x 2 = 2 Al=1 x 2 = 2 Mg= 1 Mg = 1 Cl= 2 x 3 = 6 Cl= 3 x 2 = 6 H= 1 x 2 = 2 Cl = 2 Cl = 1 x 2 = 2 H=2 f. 4Fe + 3O2 → 2Fe2O3 n. 2Na + 2HCl → 2NaCl + 2H2 Fe = 1 x 4 = 4 Fe= 2 x 2 = 4 Na= 1 x 2 = 2 Na = 1 x 2 = 2 O= 2 x 3 = 6 O= 3 x 2 = 6 H= 1 x 2 = 2 Cl = 1 x 2 = 2 Cl = 1 x 2 = 2 H=2 g. N2 + O2 → 2NO o. 2Al + 6HCl → 2AlCl3 + 3H2 N=2 N=1x2=2 Al= 1 x 2 = 2 Al = 1 x 2 = 2 O=2 O=1x2=2 H= 1 x 6 = 6 Cl = 3 x 2 = 6 Cl = 1 x 6 = 6 H=2x3=6 Note: All these exercises are important. + Remember to focus on the following: - Electron configuration (KLMN / octet rule / elements gain or lose electrons) - difference between cations and anions - difference between physical and chemical change - law of conservation of mass - difference between transverse and longitudinal waves - mind map about waves (electromagnetic – mechanical – longitudinal – transvers) - labeling of a wave