a chemist takes 100 ml of a 40 ml nacl solution she then dilutes it to 1l what is the concentration molarity of the new solution

HESI A2

Chemistry Hesi A2

1. A chemist takes 100 mL of a 40 g NaCl solution and dilutes it to 1L. What is the concentration (molarity) of the new solution?

A. 0.04 M NaCl
B. 0.25 M NaCl
C. 0.40 M NaCl
D. 2.5 M NaCl

Correct answer: C

Rationale: Initially, the chemist has 40 g of NaCl in 100 mL of solution. To find the initial molarity, we need to calculate the number of moles of NaCl using the molar mass of NaCl (58.44 g/mol). After dilution to 1 L, the molarity of the new solution can be calculated by dividing the moles of NaCl by the total volume in liters. Therefore, the concentration (molarity) of the new solution is 0.40 M NaCl. Choice A (0.04 M NaCl) is incorrect because it doesn't consider the correct molar concentration after dilution. Choice B (0.25 M NaCl) is incorrect as it also doesn't account for the correct molar concentration post-dilution. Choice D (2.5 M NaCl) is incorrect as it is too concentrated given the initial amount of NaCl and the dilution factor.

2. Where would you expect tap water to fall on the pH scale?

A. Between 1 and 3
B. Between 4 and 6
C. Between 6 and 8
D. Between 8 and 10

Correct answer: C

Rationale: Tap water typically falls within the pH range of 6 to 8, making it slightly acidic to neutral. Most municipal water systems aim to provide water that is safe for consumption and falls within this pH range. A pH level of 7 is considered neutral, so tap water may vary slightly on either side of this number but typically remains within the 6 to 8 range to ensure it is safe for consumption. Choices A, B, and D are incorrect because tap water is not expected to have a pH as low as 1-3 (highly acidic) or as high as 8-10 (alkaline); it usually falls within the slightly acidic to neutral range, hence falling between 6 and 8 on the pH scale.

3. Which of these elements has the greatest atomic mass?

A. Au
B. Ba
C. I
D. W

Correct answer: D

Rationale: Among the elements listed, Tungsten (W) has the greatest atomic mass. The atomic mass of Tungsten is approximately 183.84 atomic mass units (amu), while the atomic masses of the other elements listed are as follows: Gold (Au) is around 196.97 amu, Barium (Ba) is approximately 137.33 amu, and Iodine (I) is about 126.90 amu. Therefore, Tungsten (W) has the greatest atomic mass out of the given elements. Gold (Au) has a higher atomic mass than Barium (Ba) and Iodine (I), making choices A, B, and C incorrect.

4. Which element has the highest electronegativity?

A. Fluorine
B. Chlorine
C. Nitrogen
D. Oxygen

Correct answer: A

Rationale: Fluorine has the highest electronegativity among the elements listed. Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. Fluorine, being the most electronegative element on the periodic table, has the strongest ability to attract electrons towards itself compared to chlorine, nitrogen, and oxygen. Therefore, fluorine is the correct answer. Chlorine, nitrogen, and oxygen have lower electronegativities compared to fluorine, making them incorrect choices for the element with the highest electronegativity.

5. What type of reaction involves atoms attempting to achieve stable electron configurations?

A. Chemical
B. Nuclear
C. Physical
D. Mechanical

Correct answer: A

Rationale: In a chemical reaction, atoms interact to achieve stable electron configurations through the formation of new chemical bonds or the breaking of existing ones. This process aims to reach a more stable state by filling or emptying electron orbitals, leading to the formation of new substances with more stable configurations. Choice B, nuclear reactions, involve changes in the atomic nucleus rather than electron configurations. Choice C, physical reactions, involve changes in physical state or appearance without changing the chemical makeup. Choice D, mechanical reactions, do not involve the rearrangement of electrons to achieve stable configurations.