Question

a 90.0g sample of nacl is dissolved in water to make a solution with a volume of 3.00 l. what is the molarity of this solution? 30.0 m 0.513 m 3.00 m 0.750 m question 37 (0.0862 points) a specific isotope has 17 protons and 18 neutrons. what is the symbol for this element? \\(_{17}^{18}\\)cl \\(_{17}^{35.45}\\)cl \\(_{18}^{17}\\)ar none of these

Explanation:

First Question (Molarity of NaCl solution)

Step1: Find moles of NaCl

Molar mass of NaCl: $Na = 22.99\ g/mol$, $Cl = 35.45\ g/mol$, so $M(NaCl) = 22.99 + 35.45 = 58.44\ g/mol$.
Moles $n = \frac{mass}{molar\ mass} = \frac{90.0\ g}{58.44\ g/mol} \approx 1.54\ mol$ (wait, no, recalculate: $90 / 58.44 \approx 1.54$? Wait, no, 58.441.5=87.66, 90-87.66=2.34, 2.34/58.44≈0.04, so ~1.54? Wait, no, wait the options are 0.513, 30, 3, 0.75. Wait, maybe I miscalculated. Wait, 90g NaCl, molar mass 58.44 g/mol. So moles = 90 / 58.44 ≈ 1.54 mol? Wait, no, 58.441.5=87.66, 90-87.66=2.34, 2.34/58.44≈0.04, so ~1.54. Then volume is 3.00 L. Molarity $M = \frac{n}{V} = \frac{1.54\ mol}{3.00\ L} ≈ 0.513\ M$. Ah, right! I messed up the division. 90 divided by 58.44 is approximately 1.54? Wait no, 58.44 1.5 = 87.66, 90 - 87.66 = 2.34, 2.34 / 58.44 ≈ 0.04, so total ~1.54? Wait, no, 90 / 58.44: let's do 90 ÷ 58.44. 58.441 = 58.44, 90-58.44=31.56. 58.44*0.5=29.22, so 1.5 + (31.56-29.22)/58.44 = 1.5 + 2.34/58.44 ≈ 1.5 + 0.04 = 1.54 mol. Then divide by 3 L: 1.54 / 3 ≈ 0.513 M. Yes, that matches the option.

Step2: Calculate molarity

Molarity $M = \frac{n}{V} = \frac{1.54\ mol}{3.00\ L} ≈ 0.513\ M$.

Step1: Identify element from protons

Protons = atomic number (Z) = 17, so element is Cl (chlorine, Z=17).

Step2: Calculate mass number (A)

Mass number $A = protons + neutrons = 17 + 18 = 35$.

Step3: Isotope symbol format

Isotope symbol: $_{Z}^{A}X$, so $_{17}^{35}Cl$? Wait, the options: first option is $_{17}^{18}Cl$ (A=18, wrong), second is $_{17}^{35.45}Cl$ (mass number is integer, 35.45 is atomic weight, wrong), third is $_{18}^{17}Ar$ (Z=18 is Ar, wrong). Wait, but 17+18=35, so correct symbol should be $_{17}^{35}Cl$, but none of the options have $_{17}^{35}Cl$? Wait the options: first is $_{17}^{18}Cl$, second is $_{17}^{35.45}Cl$, third is $_{18}^{17}Ar$, fourth is none of these. Wait, mass number is 35, so the correct symbol is $_{17}^{35}Cl$, but the options don't have that. So the answer is "none of these"? Wait, no, wait the second option is $_{17}^{35.45}Cl$ – but mass number must be integer (sum of protons and neutrons, 17+18=35). So 35.45 is atomic mass, not mass number. So the correct isotope symbol should be $_{17}^{35}Cl$, which is not listed. So the answer is "none of these".

Answer:

0.513 M (the option with 0.513 M)

Second Question (Isotope symbol)