Solution:

Given:
Mass of formic acid (HCOOH) = 2.3g
Mass of oxalic acid (H2C2O4) = 4.5g

Step 1: Calculate the number of moles of formic acid and oxalic acid

To calculate the number of moles, we use the formula:
Number of moles = Mass / Molar mass

The molar mass of formic acid (HCOOH) = 1 + 12 + 16 + 16 + 1 = 46 g/mol
Number of moles of formic acid = 2.3g / 46 g/mol = 0.05 mol

The molar mass of oxalic acid (H2C2O4) = 2 + 12 + 12 + 16 + 16 + 16 + 16 + 1 + 1 = 90 g/mol
Number of moles of oxalic acid = 4.5g / 90 g/mol = 0.05 mol

Step 2: Determine the balanced chemical equation

The balanced chemical equation for the reaction of formic acid and oxalic acid with concentrated sulfuric acid (H2SO4) is:
HCOOH + H2C2O4 → CO2 + CO + H2O

Step 3: Calculate the moles of the evolved gases

From the balanced equation, we can see that for every 1 mole of formic acid and oxalic acid, 2 moles of carbon dioxide (CO2) and 1 mole of carbon monoxide (CO) are produced. Therefore, the total number of moles of carbon dioxide and carbon monoxide produced can be calculated as follows:

Moles of CO2 = 2 * 0.05 mol = 0.1 mol
Moles of CO = 1 * 0.05 mol = 0.05 mol

Step 4: Calculate the weight of the remaining product

The weight of the remaining product can be determined by subtracting the weight of the evolved gases from the initial mass of the mixture.

The molar mass of carbon dioxide (CO2) = 12 + 16 + 16 = 44 g/mol
The molar mass of carbon monoxide (CO) = 12 + 16 = 28 g/mol

Weight of CO2 = Moles of CO2 * Molar mass of CO2 = 0.1 mol * 44 g/mol = 4.4 g
Weight of CO = Moles of CO * Molar mass of CO = 0.05 mol * 28 g/mol = 1.4 g

Weight of the remaining product = Initial mass of the mixture - Weight of evolved gases
= (2.3g + 4.5g) - (4.4g + 1.4g) = 1.4g

Therefore, the weight of the remaining product at STP will be 1.4g.