Question

1. Which of the following represents a 0.100 mol/L KCI solution?

a) 1000 mL of solution containing 74.6 g KCI b)100 g KCI in 1.00 L of solution

c)5.00 L of solution containing 373 g KCI

d) 7.46 mg KCl per mL of solution

You place a 4.00 kg iron bar (specific heat capacity, C: 0.4 water at 23.0 ℃ (density = 0.998 g/mL, C, = 4.184 J/g。C). After several minutes, the temperature of the water is 28.7 'C. What was the initial temperature of the iron bar?

Neutral atoms with the outer electron configuration ns'np in their lowest energy (ground) states belong to the group with elements: 4. B, Al, Ga, In b. Li, Na, K, Rbc. Cu, Ag, Au d. Sc, Y, La

Answer 1

1) Molar mass of KCl = 74.5516 g/mol

mass (m) = 7.46 mg = 0.00746 g

now, moles of KCl= mass / molar mass = 0.00746 g / 74.5516gmol^-1 = 0.0001 mol

Now, 1 ml = 0.001 L

So molarity , M = 0.0001 moles KCl / 0.001 L = 0.100 mol /L KCl

The answer will be d) d) 7.46 mg KCl per mL of solution .

2) mass of water = 1 kg = 1000 g ( not mentioned) , mass of iron = 4 kg = 4000 g

Heat lost by metal (iron) = heat gained by iron

=> m x C_iron x T = m x C_water x T

=> 4000 g x 0.473 J/g⁰C x ( x - 28.7)⁰C = 1000 g x 4.184 J/g⁰C x (28.7 - 23.0 )⁰C

=> 1892 (x - 28.7) = 23848.8

=> x -28.7 = 23848.8 /1892

=> x -28.7 = 12.60

=> x = 12.60 +28.7 = 41.3⁰C

[ The x - 28.7 ⁰C is the T of the iron. It went from a hot temperature 'x' to a cooler temperature of 28.7⁰C.]

3) Neutral atoms with the outer electron configuration ns²np¹ in their lowest energy (ground) states belong to the group III A elements. namely boron (B) , aluminium (Al) , gallium (Ga) , indium (In) and thallium ( Tl)

So, the answer will be -- a) B, Al, Ga, In.