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# During a laboratory activity, appropriate safety equipment is used and safety procedures are followe

NY Regents Chemistry Exam Jan 2023

During a laboratory activity, appropriate safety equipment is used and safety procedures are followed. A student uses the lab equipment shown in the diagram below to determine the heat of combustion of candle wax.

Heat of combustion is defined as the amount of heat released when a known mass of a substance is burned and can be measured in joules per gram. At the start of the activity, the mass of the candle and the mass of the water are measured. The starting temperature of the water is 5.0°C, and the air temperature in the room is 22.0°C. The candle is lit, and the water is stirred with a stirring rod. Several minutes later, the candle is extinguished, and the student measures the temperature of the water in the can. When the candle is cool, the student measures the final mass of the candle. Lab activity results are shown in the table below. 69. State the number of significant figures used to express the value for the mass of the water in the can. 

All the numbers are zeroes after a number are significant. The mass is expressed as 190. 1,9 and 0 here are significant.

70. State the direction of the heat flow between the air and the water in the can before the candle is lit. 

Let's take a look at the temperature of the air and water. As the question states the starting temperature of the water is 5.0°C, and the air temperature in the room is 22.0°C. Heat flows from higher to lower temperature.

Answer: Heat flows from the air to the water

71. Determine the amount of heat absorbed by the water. 

Table T on the Reference Table gives equations for calculating heat amount. q=mcΔT.

mass is 190g from the chart.

ΔT is 39C from the chart.

Specific heat capacity (c) is 4.18 J/gC from the Reference Table, Table b.

q = (190g)(4.18 J/gC)(39C)