Sample Questions in multiple choice format.

Transcription

1 Sample Questions in multiple choice format. 1. Which among the following statements is false? A) A solid has a definite shape and a definite volume. B) A liquid has a definite volume; but it has no definite shape. C) A gas has neither definite volume nor definite shape. D) Both solids and liquids are incompressible while gases are compressible. 2. Which of the following is a heterogenous mixture? A) milk B) sugar water C) raisin bran D) air 3. A solution is an example of a (an) A) pure substance B) element C) compound D) homogeneous mixture E) heterogeneous mixture 4. Which statement below best describes the process of the paint on a vehicle fading over time? A) Chemical change because the paint molecules are changing composition. B) Physical change because the paint molecules are still paint molecules. C) Chemical change because the paint molecules are changing phases. D) Physical change because the paint molecules have risen to the surface of the clear coat finish. 5. When methane is burned with oxygen the products are carbon dioxide and water. If you produce 36 grams of water and 44 grams of carbon dioxide from 16 grams of methane, how many grams of oxygen were needed for the reaction? A) 32 B) 0 C) 96 D) 64 (law of conservation of mass. Total mass of chemicals used before reaction equals total mass of chemicals produced after reaction). *** Match this with your Lab EXP: Think about your sand and salt separation experiment. Your final separated, recovered weight of your salt AND sand should match the weight of mixture you started with. It is up to you to get more or less based on how well you dried them, or if you spilled the solution, or you didn t get all the sand out on to the filter paper etc these are called experimental errors.) 6. How many joules are there in a 255 calorie snack bar? 5 A) B) C) D) A 15.0 gram lead ball at 25.0 C was heated with 40.5 joules of heat. Given the specific heat of lead is 0.12 J / g g C, what is the final temperature of the lead? A) 21.1 C B) 46.1 C C) 77. C D) 0.44 C. Consider the following specific heats of metals. Metal Specific Heat (J/g C) Aluminum Copper 0.35 Gold 0.12 Iron Silver If the same amount of heat is added to 50.0 g samples of each of the metals, which are all at the same temperature, which metal will reach the highest temperature? A) aluminum 1

2 B) copper C) gold D) iron E) silver 9. Mg is a member of which family? A) noble gases B) halogens C) alkaline earth metals D) alkali metals 10. What is the charge on an ion that has an atomic number of 27 and contains 26 e? A) 1+ B) 1- C) 2- D) An atom of a carbon-14 isotope would contain A) 6 protons, neutrons,and 6 electrons. B) protons, 6 neutrons,and electrons. C) 6 protons, neutrons,and electrons. D) 14 protons, 6 neutrons,and 6 electrons. E) 20 protons, 6 neutrons,and 20 electrons. 12. Another atom that has the same number of neutrons as 13 is: A) Cs B) Ba C) La 56 Ba D) Xe ( to calculate number of neutrons, subtract atomic number from mass number.) 13. A fictional element has two isotopes, each making up 50% of the population. Isotope 1 has a mass of 0.0 amu, Isotope 2 has a mass of 5.0 amu. Calculate the atomic mass of the fictional element. A) 2.5 amu B) 42.5 amu C) 40 amu D) 165 amu Show all calculations using significant figures and units correctly to receive full credit An unknown metal is suspected to be gold. When 2. J of heat are added to 5.6 g of the metal, its temperature raises by 3.9 o C. How do you conclude if the metal is gold from the data? (sp heat of gold: cal/g. o C) Given: q = 2. J, mass = 5.6 g; T = 3.9 o C solve for specific heat of the metal C? Use q = m. C. T and find C in J/g. o C = 0.13 J/g o C Convert J/ g. o C to cal / g.oc [ use 1 cal = 4.14 J] Answer: Yes, it is gold. C = cal/g. o C 2

3 3.97 A backpacker wants to carry enough fuel to heat 2.5 kg of water from 25 o C to 100 o C. If the fuel he carries produces 36 kj of heat per gram when it burns, how much fuel should he carry? (Assume all the fuel will be consumed with 100% efficiency) Before you calculate how much fuel he needs to carry, you need to know how much heat he needs to generate for the 2.5 kg of water he will be using. Once you have calculated the heat q, use the fuel efficiency of the stove (36 kj/gram) to find out how much fuel he needs to carry. STEP 1. Calculate amount of heat needed to heat water using: q = m. C. T Mass, m = 2.5 X 10 3 g (converted to g, keeping 2 significant figures); Sp. Heat C (of water) = 4.14 J / g. o C (use value of specific heat C in Joules because the fuel efficiency is given in J ) T = (100 25) o C = 75 o C, remember T is T final T initial q = 2.5 X 10 3 g X 4.14 J /g. o C X 75 o C q = 7. X 10 5 J STEP 2. use the fuel efficiency to find fuel in grams: 7. X 10 5 J X 1 g X 1 kj 36 kj 1 X 10 3 J Answer: 21. g = 22 g (rounded) 3

4 Calculate how much heat would be required to warm up Earth s oceans by 1.0 o C. Assume that the volume of Earth s oceans is 137X10 3 km 3 and the density of seawater is 1.03 g/cm 3. We are also assuming that the heat capacity of seawater is same as water. Given: Density = 1.03 g/cm 3 Volume = 137 X 10 3 km 3 T = 1.0 o C Specific heat C = 1.0 cal / g. o C ( we are asked to assume this) STEP 1. Before you calculate heat you need to calculate the mass using the given volume and density data 1 km = 1 X 10 5 cm ( cube both sides) 1 km 3 = (1 X 10 5 cm) 3 = 1 X cm 3 volume = 137X10 3 km 3 X [1X10 15 cm 3 / 1 km 3 ] = 137 X 10 1 cm 3 mass = vol X density = 137X10 1 cm 3 X 1.03 g/cm 3 =1.41 X 10 1 g STEP 2. We can now calculate heat q, using mass (m) we calculated in STEP 1 q = mass X C X T = 1.41X10 1 g X 1.0 cal / g. o C X 1.0 o C = 1. 4X10 1 cal (rounded to 2 s.f) * Interesting concept question. This has to do with high heat capacity of water. San Francisco is near the ocean which regulates and maintains a more consistent temperature, unlike Sacramento which is further inland. 4.9 Write the isotopic symbol/s for the oxygen isotope with neutrons 16 O 4.91 U-235 (U = Uranium). Write the symbol of the isotope U 4

5 Pb (Pb = lead). Determine number of protons and neutrons. Protons = 2 (atomic number) Neutrons = mass number atomic number = 20 2 = An element has two naturally occurring isotopes. Isotope 1 has a mass of amu and a relative abundance of 57.4%, and isotope 2 has a mass of amu and a relative abundance of 42.6%. Find the atomic mass of this element and identify the element from the periodic table. Atomic mass of element = mass of I1 X percent abundance of I1 + mass of I2 X percent abundance of I2 Atomic mass of element = amu X 57.4% amu X 42.6% = 69.4 amu amu = 121. amu The element is Sb (antimony, Latin Stibium) Z = Atomic Number (Read directly from Periodic Table) = number of protons A= Mass Number = number protons + number neutrons Note: The number of protons do not change when an ion forms, it is fixed for an element, and equals the Atomic Number. Only number of electrons changes in the ion when compared with the neutral element. Symbol Z A #protons #electrons #neutrons charge Mg O Ga