Aresearcher dispenses distilled deionized water from a 20-ml volumetric pipet into an empty 8.4376 g weighting bottle. if the total mass of water and weighting bottle is 28.5845 g, what is the volume of the water delivered by the 20-ml pipet? the density of water is 0.9967867 g/ml.

As given that some volume of water has been dispensed say "x mL"

The initial weight of bottle =8.4376 g

The final weight of bottle + water =28.5845 g

So weight of water transferred = 28.5845 g - 8.4376 g = 20.1469 g

Now there is a relation between density, mass and volume

density = mass / volume

Therefore

Volume = mass / density

So volume of water dispensed = mass dispensed / density =20.1469 g / 0.9967867 g/ml.

Volume of water = 20.2118467 mL

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8