Which explains the basis of the biuret test? a. under base conditions, copper ions bind to the amino groups of proteins and change color. b. iodine fits into the coils of starch polymers and changes color. c. a blue dye binds to protein and changes color. d. sudan iii dye binds to lipids and changes color.

A

Explanation:

In the Biuret test, the copper ions bind covalently to the amino groups as shown in the image to form a violet complex. This violet complex is responsible for the colour change as shown

Under base conditions, copper ions bind to amino groups of proteins and change colour.

Explanation: Biuret test is a general test for detecting the presence of a peptide bond in a compound. It is a test for proteins. Amino acids are joined together in proteins by peptide bonds. Copper ions from blue alkaline solution of CuSO4 react with amino groups of proteins to give a violet colored complex called a biuret compound

answer: mercury

explanation:

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