Basic Concepts Of Chemistry

1.

A measured temperature on Fahrenheit scale is 200°F. What will this reading be on celsius scale?
- A.
  
  40°C
- B.
  
  94°C
- C.
  
  93.3°C
- D.
  
  30°C
Correct Answer
C. 93.3°C

Explanation
To convert a temperature from Fahrenheit to Celsius, you can use the formula: C = (F - 32) * 5/9. Plugging in the given temperature of 200°F into the formula, we get: C = (200 - 32) * 5/9 = 168 * 5/9 = 840/9 = 93.3°C. Therefore, the correct answer is 93.3°C.

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2.

What will be the molarity of a solution, which contains 5.85 g of NaCl per 500 mL ?
- A.
  
  4 mol/L
- B.
  
  20 mol/L
- C.
  
  0.2 mol/L
- D.
  
  2 mol/L
Correct Answer
C. 0.2 mol/L

Explanation
The molarity of a solution is calculated by dividing the moles of solute by the volume of the solution in liters. In this case, we are given the mass of NaCl (5.85 g) and the volume of the solution (500 mL). To find the moles of NaCl, we need to convert the mass to moles using the molar mass of NaCl (58.44 g/mol). The moles of NaCl can be calculated as 5.85 g / 58.44 g/mol = 0.1 mol. Since the volume is given in mL, we need to convert it to liters by dividing by 1000. So, the volume of the solution is 500 mL / 1000 = 0.5 L. Finally, we can calculate the molarity by dividing the moles of NaCl (0.1 mol) by the volume of the solution (0.5 L), which gives us 0.2 mol/L.

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3.

If the concentration of glucose in blood is 0.9 g/L, what will be the molarity of glucose in blood?
- A.
  
  5 M
- B.
  
  50 M
- C.
  
  0.005 M
- D.
  
  0.5 M
Correct Answer
C. 0.005 M

Explanation
The molarity of a solution is calculated by dividing the moles of solute by the volume of the solution in liters. In this case, the concentration of glucose in blood is given as 0.9 g/L. To find the molarity, we need to convert grams to moles. The molar mass of glucose is approximately 180 g/mol. Therefore, the number of moles of glucose in 0.9 g is 0.9/180 = 0.005 mol. Since the volume is not given, we cannot calculate the exact molarity. However, based on the given options, the closest value is 0.005 M.

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4.

What will be the molality of the solution containing 18.25 g of HCl gas in 500 g of water ?
- A.
  
  0.1 m
- B.
  
  1 M
- C.
  
  0.5 m
- D.
  
  1 m
Correct Answer
D. 1 m

Explanation
The molality of a solution is calculated by dividing the moles of solute by the mass of the solvent in kilograms. In this case, we need to convert the mass of HCl gas to moles using its molar mass and then divide by the mass of water in kilograms. Since the answer is given as 1 m, it means that the molality of the solution is 1 mole of HCl per kilogram of water.

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5.

What is the mass percent of carbon in carbon-di-oxide ?
- A.
  
  0.034 %
- B.
  
  27.27 %
- C.
  
  3.4 %
- D.
  
  28.70 %
Correct Answer
B. 27.27 %

Explanation
Carbon dioxide (CO2) is composed of one carbon atom and two oxygen atoms. To calculate the mass percent of carbon in CO2, we need to determine the mass of carbon in one molecule of CO2 and divide it by the molar mass of CO2. The molar mass of carbon is 12.01 g/mol, and the molar mass of CO2 is 44.01 g/mol. The mass of carbon in one molecule of CO2 is 12.01 g. Dividing 12.01 g by 44.01 g/mol and multiplying by 100 gives us approximately 27.27%. Therefore, the mass percent of carbon in carbon dioxide is 27.27%.

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6.

The empirical formula and molecular mass of a compound are CH₂O and 180 g respectively. What will be the molecular formula of the compound ?
- A.
  
  C₉H₁₈O₉
- B.
  
  CH₂O
- C.
  
  C₆H₁₂O₆
- D.
  
  C₂H₄O₂
Correct Answer
C. C₆H₁₂O₆

Explanation
The empirical formula CH2O indicates that the compound contains one carbon atom, two hydrogen atoms, and one oxygen atom. The molecular mass of 180 g suggests that the compound's molecular formula must have a mass of 180 g. The molecular formula C6H12O6 satisfies both conditions, as it has a molecular mass of 180 g and contains the same ratio of carbon, hydrogen, and oxygen atoms as the empirical formula. Therefore, the molecular formula of the compound is C6H12O6.

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7.

An element X has the following isotropic composition: ²⁰⁰X: : 90% , ¹⁹⁹X: 8.0% , ²⁰²X: 2.0% , The weighted average atomic mass of the naturally occurring element X is closest to:
- A.
  
  199 amu
- B.
  
  200 amu
- C.
  
  201 amu
- D.
  
  202 amu
Correct Answer
B. 200 amu

Explanation
The weighted average atomic mass of element X is closest to 200 amu because it is the most abundant isotope with a composition of 90%. The other isotopes, 199X and 202X, have compositions of 8.0% and 2.0% respectively. By calculating the weighted average, taking into account the abundance and mass of each isotope, the closest value is 200 amu.

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8.

How many moles of electrons weigh one Kg?
- A.
  
  6.023 x 10^23
- B.
  
  1/9.108 x 10^31
- C.
  
  6.023/9.108 x 10^54
- D.
  
  1/(9.108 x 9.023) x 10^8
Correct Answer
D. 1/(9.108 x 9.023) x 10^8
9.

The total number of atoms of all elements present in mole of ammonium dichromate is
- A.
  
  19
- B.
  
  6.023 x 10^23
- C.
  
  114.473 x 10^23
- D.
  
  84.332 x 10^23
Correct Answer
C. 114.473 x 10^23

Explanation
Ammonium dichromate has the chemical formula (NH4)2Cr2O7. By counting the atoms in this formula, we can determine the total number of atoms present in one mole of ammonium dichromate. The formula contains 2 nitrogen atoms (N), 8 hydrogen atoms (H), 2 chromium atoms (Cr), and 7 oxygen atoms (O). Adding these numbers together gives a total of 19 atoms. Therefore, the correct answer is 19.

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10.

Which has the maximum number of molecules among the following?
- A.
  
  44 g of CO2
- B.
  
  48 g of O2
- C.
  
  8g of H2
- D.
  
  64 g of SO2
Correct Answer
C. 8g of H2

Explanation
The number of molecules in a substance can be determined by using Avogadro's number and the molar mass of the substance. The molar mass of CO2 is 44 g/mol, the molar mass of O2 is 32 g/mol, the molar mass of H2 is 2 g/mol, and the molar mass of SO2 is 64 g/mol. Since the molar mass of H2 is the smallest among the given substances, 8 g of H2 will have the maximum number of molecules.

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Basic Concepts Of Chemistry

A measured temperature on Fahrenheit scale is 200°F. What will this reading be on celsius scale?

What will be the molarity of a solution, which contains 5.85 g of NaCl per 500 mL ?

If the concentration of glucose in blood is 0.9 g/L, what will be the molarity of glucose in blood?

What will be the molality of the solution containing 18.25 g of HCl gas in 500 g of water ?

What is the mass percent of carbon in carbon-di-oxide ?

The empirical formula and molecular mass of a compound are CH2O and 180 g respectively. What will be the molecular formula of the compound ?

An element X has the following isotropic composition: 200X: : 90% , 199X: 8.0% , 202X: 2.0% , The weighted average atomic mass of the naturally occurring element X is closest to:

How many moles of electrons weigh one Kg?

The total number of atoms of all elements present in mole of ammonium dichromate is

Which has the maximum number of molecules among the following?

The empirical formula and molecular mass of a compound are CH₂O and 180 g respectively. What will be the molecular formula of the compound ?

An element X has the following isotropic composition: ²⁰⁰X: : 90% , ¹⁹⁹X: 8.0% , ²⁰²X: 2.0% , The weighted average atomic mass of the naturally occurring element X is closest to: