Which is an example of making a quantitative observation?
measuring the mass of metal used in a reaction
recording the color of a solid formed in a reaction
describing a liquid as having a slippery feel
rating an odor on how nice it smells

measuring the mass of metal used in a reaction

Explanation:

In chemistry we analyse any matter in two ways

a) Qualitative: For qualitative analysis we study quality of matter which includes

i) its chemical nature: example organic / inorganic/ cation /anion/ acid/ base / aromatic/ cyclic etc.

ii) its physical nature : example color, odor , viscosity. lubricity, density, temperature, pressure etc.

b) Quantitative: For quantitative analysis we study the quantity of matter.

For example

Mass or volume or mole or concentration etc.

So here measuring the mass of metal used in a reaction is a quantitative observation.

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