1.
Convert 3.4*10^6 nm→km.
Correct Answer
C. 3.4*10^-6
Explanation
To convert from nanometers (nm) to kilometers (km), we need to move the decimal point 9 places to the left since there are 10^9 nanometers in a kilometer. Therefore, the correct answer is 3.4*10^-6 km.
2.
Boiling point of liquid nitrogen is(-252.87C°), what is the boiling expressed on the Kelvin scale?
Correct Answer
A. 20.13 k
Explanation
The boiling point of liquid nitrogen is -252.87°C. To convert this temperature to the Kelvin scale, we need to add 273.15 to the Celsius temperature. Thus, -252.87°C + 273.15 = 20.28 K. The closest option to this value is 20.13 k, which is the correct answer.
3.
The SI-unit for density is?
Correct Answer
D. Kg/m^3
Explanation
The SI unit for density is kilograms per cubic meter (kg/m^3). Density is defined as the mass of an object divided by its volume. The unit of mass is kilograms (kg) and the unit of volume is cubic meters (m^3). Therefore, the correct unit for density is kg/m^3.
4.
Which of the masses below is the smallest?
Correct Answer
A. 2.5*10^-3 ng
Explanation
The given answer 2.5*10^-3 ng is the smallest mass among the options provided. This is because the negative exponent indicates a very small value. In this case, -3 as the exponent means that the value is divided by 1000 three times, resulting in a smaller mass compared to the other options.
5.
How many significant figures should be in the final answer for this calculation (5.657-2.33)?
Correct Answer
A. 3
Explanation
The calculation involves subtracting two numbers, 5.657 and 2.33. The number with the fewest decimal places is 2.33, which has 2 significant figures. Therefore, the final answer should also have 2 significant figures.
6.
How many (mg)are there in 2.5*10^-3 of CH3COOH?
Correct Answer
B. 150
Explanation
The question asks for the amount of CH3COOH in milligrams. To convert from moles to milligrams, we need to use the molar mass of CH3COOH, which is approximately 60.05 g/mol. Since 1 mole of any substance is equal to its molar mass in grams, we can multiply the given amount (2.5*10^-3 moles) by the molar mass (60.05 g/mol) to get the answer in grams. Finally, we convert grams to milligrams by multiplying by 1000. Therefore, the correct answer is 150 mg.
7.
How many Floride atoms are there in 25g AlF3?
Correct Answer
B. 5.3*10^23
Explanation
The answer 5.3*10^23 suggests that there are approximately 5.3*10^23 fluoride atoms in 25g of AlF3. This can be determined by calculating the number of moles of AlF3 using its molar mass, and then multiplying this by Avogadro's number to find the number of fluoride atoms.
8.
An unknown compound has on empirical Formula of C3H4 the molar mass of the compound is 120 g/mol, what is the molecular formula?
Correct Answer
C. C9H12
Explanation
The empirical formula of the unknown compound is C3H4, which means that the compound contains 3 carbon atoms and 4 hydrogen atoms in its simplest ratio. The molar mass of the compound is given as 120 g/mol. To determine the molecular formula, we need to find the ratio between the empirical formula mass and the molar mass. The empirical formula mass can be calculated by adding the atomic masses of the atoms in the empirical formula, which in this case is (3 * atomic mass of carbon) + (4 * atomic mass of hydrogen). If we divide the molar mass by the empirical formula mass, we get a ratio of 40. Since the ratio is 3, it means that the molecular formula is three times the empirical formula, which gives us C9H12.
9.
In this reaction S+CL2——->SCL2, if the grams of S (16g) and the Grams of CL2 is (7.1g). How many grams of sulfur, is left unreacted?
Correct Answer
C. 12.8g
Explanation
In the given reaction, the balanced equation is S + Cl2 -> SCl2. According to the equation, 1 mole of S reacts with 1 mole of Cl2 to form 1 mole of SCl2. The molar mass of S is 32 g/mol, and the molar mass of Cl2 is 70.9 g/mol.
Using the given masses, we can calculate the number of moles of S and Cl2. The number of moles of S is 16g/32g/mol = 0.5 mol, and the number of moles of Cl2 is 7.1g/70.9g/mol = 0.1 mol.
Since the reaction is a 1:1 ratio, the limiting reactant is Cl2, and it will completely react with 0.1 mol of S. Therefore, 0.4 mol of S will be left unreacted.
The mass of the unreacted S can be calculated by multiplying the number of moles by the molar mass: 0.4 mol * 32 g/mol = 12.8g. Therefore, the correct answer is 12.8g.
10.
In the last question if 3.5g of SCL2 were produced by experiment,what is the present yield of SCL2?
Correct Answer
B. 34%
Explanation
The present yield of SCL2 is 34%. This means that out of the total amount that could have been produced, only 34% was actually obtained in the experiment. This indicates that the experiment did not yield a high amount of SCL2, suggesting that there may have been factors that hindered the production or collection of the compound.
11.
Calculate the molecules of CO2 produced when 58g C4H10 are reacted with 4g O2 according to the equation:
C4H10 +13/2 O2—-> 4CO2+5H2O
Correct Answer
C. 0.46 *10^23 molecule
Explanation
The balanced equation shows that for every 1 mole of C4H10 reacted, 4 moles of CO2 are produced. To find the number of molecules of CO2 produced, we need to convert the given mass of C4H10 to moles, and then use the mole ratio from the balanced equation to find the number of moles of CO2. Finally, we convert the moles of CO2 to molecules using Avogadro's number. The correct answer of 0.46 *10^23 molecules is obtained through this calculation.
12.
Calculate the mass of NaCl produce when 10g of NaOH are reacted (100ml,0.1M)of HCL according to the equation :
NaOH+HCL—->NaCL+H2O
Correct Answer
A. 0.585g
Explanation
When 10g of NaOH reacts with HCl according to the given equation, the balanced equation tells us that 1 mole of NaOH reacts with 1 mole of HCl to produce 1 mole of NaCl. The molar mass of NaOH is 40 g/mol, so 10g of NaOH is equivalent to 0.25 moles. Since the reaction is 1:1, the moles of NaCl produced will also be 0.25. The molar mass of NaCl is 58.5 g/mol, so the mass of NaCl produced will be 0.25 moles multiplied by 58.5 g/mol, which equals 0.585g. Therefore, the correct answer is 0.585g.
13.
How many grams of Ca(OH)2 are required for 200 ml of 0.3 HCL solution:
Ca(OH)2+2HCL—->2H2O+CaCL2
Correct Answer
D. 2.22g
Explanation
To determine the grams of Ca(OH)2 required, we need to use the balanced equation and the molar ratio between Ca(OH)2 and HCl. From the equation, we can see that 1 mole of Ca(OH)2 reacts with 2 moles of HCl. To find the moles of HCl in the 200 ml solution, we multiply the volume (in L) by the molarity of HCl. Then, using the molar ratio, we can calculate the moles of Ca(OH)2 required. Finally, we convert the moles of Ca(OH)2 to grams using its molar mass. The calculation yields 2.22g of Ca(OH)2 required.
14.
Which of the following transition has the highest wavelength?
Correct Answer
C. N=3—->N=4
Explanation
The transition from N=3 to N=4 has the highest wavelength because as the electron moves from a higher energy level (N=4) to a lower energy level (N=3), it releases energy in the form of light. The wavelength of the emitted light is inversely proportional to the energy difference between the two levels. Since the energy difference between N=3 and N=4 is the largest among the given options, the wavelength of the emitted light will be the highest.
15.
Find the wave length of light emitted by a hydrogen atom during transition of it’s electron from N=1 to the N=4 principal energy level:
Correct Answer
B. 0.98*10^-7 m
Explanation
The wavelength of light emitted during the transition of an electron from one energy level to another can be calculated using the Rydberg formula. The formula is given by 1/λ = R(1/n1^2 - 1/n2^2), where λ is the wavelength, R is the Rydberg constant, and n1 and n2 are the initial and final energy levels respectively. In this case, the electron is transitioning from the N=1 to the N=4 energy level. Plugging these values into the formula, we find that the wavelength is 0.98*10^-7 m.
16.
Is the Periodic Table?
Correct Answer
A. True
Explanation
The given question is incomplete and not readable, as it is not clear what is being asked about the Periodic Table. Therefore, an explanation cannot be generated.